optimization and evaluation of an energy-efficient mac [email protected] joint work...
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IntroductionOur contribution
Experimental results
Optimization and Evaluation of an Energy-EfficientMAC protocol for WASNs
Oliviero Rganelli
School of Science and Technology,University of Camerino,62032 Camerino, Italy
Joint work withFlavio Corradini, Michele Papalini and Alberto Polzonetti
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
What is a WASN?
A Wireless Ad hoc Sensor Network (WASN) is a collection ofdevices (nodes) sensing the physical environment
It is a kind of wireless network operating in absence of apreexisting communication infrastructure
WASN are decentralized and all network activities areexecuted by nodes themselves (e.g. routing)
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
The energy problem
Devices are typically powered by batteries and devices runningout of battery power impact network functionalities
The main sources of energy waste are:Collision
two or more packets are transmitted at the same time
Overhearing
a node receives packets intended for other nodes
Overhead
energy consumed in transmitting and receiving controlmessages
Idle Listening
Listening when there is no activity in the radio channel
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
The latency problem
In a WASN, nodes use multi-hop communication to forwardtheir dataSeveral MAC protocols have employed low duty cycleoperations with a sleep/wake-up scheduling to save energyThis increases latency for the nodes on the communicationpath
when a packet arrives at a sensor node it must be queued ifthe next-hop is sleeping
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
Low duty cycle protocols
Low duty cycle protocols are essential for efficient long-termfunctioning of WASNs
Each node goes to periodic sleep mode for some time duringwhich it turns off its radio offWhen the time expires, it wakes up and listens to see if anyother node wants to communicateThe ratio of wake-up duration to the whole duration of aframe is called duty cycle
Setting a low duty cycle is possible to save energy.
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
S-MAC
S-MAC is a well known energy efficient MAC for wirelesssensor networks
Nodes go to sleep periodically by using a fixed duty cycleNeighboring nodes synchronize their schedules to reduce thecontrol overheadMessage passing is used to reduce the contention latency andcontrol overhead
Major drawbacks:
high latency if the traffic is high: nodes cannot forward all themessages in their wake-up periodenergy waste if the traffic is low: nodes stay in idle listening
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
T-MAC
Timeout-MAC (T-MAC) introduces the adaptive duty-cycleby dynamically setting the wake-up period:
At every frame the node wakes up only for a very short time(15ms vs 300ms of S-MAC)If nothing happen nodes go back to sleep stateIf an activation event (e.g. communication) is detected, nodesremain in the wake-up mode for other 15ms
Main drawbacks:
T-MAC is subject at the early sleeping problem where a nodegoes to sleep when a neighbor still has messages for itT-MAC suffers the same high latency as S-MAC when theduty-cycle is very low
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
ContextProblemRelated WorksObjective
Goal
The aim of this work is to develop a novel MAC protocol:using only local neighborhood informationreducing the energy waste due to collision and overhearingusing traffic information in order to adapt the duty-cycleimproving the balance between end-to-end latency and energyconsumption
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Basic Idea
A wake-up adaptation scheme based on model-basedpredictive control is developed
During periods of regular activity, nodes produce less traffic ascompared to periods of abnormal signal activityBy scaling down the wake-up time at regular periods, weexpect a lower energy consumption while limiting latencyAt each frame, the optimal duty-cycle is calculated bypredicting future traffic conditions
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Protocol phases
The protocol is characterized by the following phases:
synchronization phaseadaptation phasewake-up phasesleep phase
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Outline
1 IntroductionContextProblemRelated WorksObjective
2 Our contributionProtocol overviewProtocol Analysis
3 Experimental results
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Synchronization
The synchronization phase is inspired by the virtual clusteringalgorithm used in S-MAC and T-MAC.
All nodes maintain and synchronize on schedules of theirneighbors
SYNC packets are exchanged to keep the nodes schedulessynchronized and compensate for clock driftsEach node listens the channel for a while waiting for a SYNCpacket from its neighborsThe node receives and follows its neighbor’s schedule bysetting its schedule to be the same.If the node receives a different schedule after it chooses itsown schedule, it adopts both schedules
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Wake-up adaptation
The protocol uses a wake-up time adaptation strategy basedon model-based predictive control
a dynamic model of the node is used to predict and guide thenode behavior in terms of remaining energy andincoming/outgoing trafficschedule is calculated in such a way to optimize a costobjective function over a future horizon
We characterize the dynamic node model using aninput-output black-box modeling technique
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Wake-up time calculation
A learned node model is used by a Sate Estimator to estimatethe node state
An optimizer computes the optimal sequence of wake-up timeby solving an optimization problem in order to trace thedesired node behavior
The first value of the computed sequence is injected into thesensor node
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
System Model
We assume that the node dynamics are unknown and so weapply an off-line system identification approach
A mathematical model is derived by analyzing input-outputrelationship of a proper experimental data set:
x(t + 1) = Ax(t) + Bu(t) + w(t)
y(t) = Cx(t) + v(t)
x(t) is the internal state of the nodeu(t) is the wake-up time - inputy(t) is the outgoing traffic, incoming traffic and the residualbattery - outputsw(t) and v(t) are disturbance due to the use of partialinformation on the neighbors state
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
State Estimation
In the black-box approach, the node state x(t) is not directlymeasurable
We need to estimate the internal state of the node given onlythe observable outputs y(t)
The Estimator is based on the Kalman filter
it is an efficient recursive filter that estimates the state of adynamic system from a series of incomplete and noisymeasurements
The estimator uses the learned state space model in order toderive the node state
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Protocol overviewProtocol Analysis
Optimizer
Assuming that the estimates of x(t) are available at time t,the optimal wake-up time is obtained by solving the followingoptimization problem
min∆u(t),...,∆u(t+C−1)
P∑l=1
‖y(t+l |t)−r(t+l)‖2R +‖∆u(t+l−1)‖2
Q
∆u(t) = u(t)− u(t − 1) is the wake up time adjustmentr(t) is the reference trajectories of the system and we use it tosteer the behavior of the nodeQ and R are weighting matricesy(t + l |t) is the predicted value of y at time t + l based on theinformation available at time t
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Simulation environment
We compared our protocol with S-MAC and T-MAC:
We have implemented our MAC protocol, called A-MAC, inthe CastaliaOur simulation model captures a wireless ad hoc sensornetwork of Mica2 motes using Chipcon CC1100We use a grid topology of 100 nodes separated by a distanceof 30mThe size of packets is setted to 100 bytes
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Optimization Problem
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Simulation 1: high traffic load
All nodes generate packets with a random delay comprisedbetween 0.1s and 2 s
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Simulation 2: low traffic load
All nodes generate packets with a random delay comprisedbetween 10 s and 15 s
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Conclusion
The results of the experimentation showed an improvment inthe balance between end-to-end latency and energyconsumption in WASNs
Future work will involve the development of
an adaptive on-line system identification process in order tocapture changing dynamics in the application contextan efficient mechanism with low control overhead in networkswith high mobility
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs
IntroductionOur contribution
Experimental results
Thank You for Your Attention
Oliviero Rganelli Optimization and Evaluation of an Energy-Efficient MAC protocol for WASNs