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
IntroductionIntroduction
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
IntroductionIntroduction
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
Schedule ID : 1Schedule Age : 0
AdoptA
Schedule ID : 2Schedule Age : 50
B’s Schedule Age : 50 > A’s Schedule Age : 0
C
Schedule ID : 2Schedule Age : 50
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
Regular listen Fast path schedule
Data transmission S-MAC
FPAFPA
Node 1
Node 2
Node 3
Node 4
Regular listen Fast path schedule
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
Regular listen Fast path schedule
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
Experimental Results - GSAExperimental Results - GSA
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
Experimental Results - GSAExperimental Results - GSA
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
Experimental Results - GSAExperimental Results - GSA
Trigger packet was not always received by the nodes and in most experiments, 18 ~ 36% failed to participate
Experimental Results - GSAExperimental Results - GSA
Experimental Results - GSAExperimental Results - GSA- : failed to active * : initial the scheduleX : use the primary schedule o : use the secondary schedule
Experimental Results - GSAExperimental Results - GSA
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%
Experimental Results - GSAExperimental Results - GSA
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
Experimental Results - FPAExperimental Results - FPA
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.
Experimental Results - FPAExperimental Results - FPA
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
Experimental Results - FPAExperimental Results - FPA
Experimental Results - FPAExperimental Results - FPA
Experimental Results - FPAExperimental Results - FPA
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
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