Prof. George [email protected]
Applied Electronics Laboratory (APEL), ECE Dept. University of PatrasIndustrial Systems Institute, RIC “ATHENA”
4th Mediterranean Conference on Embedded ComputingMECO 2015, Budva, Montenegro, June 14-18, 2015
Challenges in the Design and Implementation of Wireless Sensor Networks: A Holistic Approach
Development and Planning Tools, Middleware,Power Efficiency, Interoperability
Keynote Speaker Presentation
Outline
Challenges for Demanding WSNsMiddleware Level FocusDevelopment Level FocusDeployment Level Focus
4th Mediterranean Conference on Embedded Computing (MECO), June 14-18, 2015, Budva, Montenegro 2
Developing and Deploying WSNs
Wireless Sensor Networks (WSNs) constitute a rapidly evolving and nearing maturity networking area with impact on various domains (i.e. environment, health, industry) Different requirements about QoS and system performance
These domains require different levels of knowledge about the mechanisms residing over the HW, i.e. Sensors, Actuators, Radio Tx/Rx, such as: Scheduling policies, algorithms, OS, security mechanismsRouting and MAC protocols
Special knowledge is required regarding characteristics such as:Constrained energy, CPU and memory resourcesMulti-hop communication
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Developing and Deploying WSNs
Incorporation of user friendliness, practicality and efficiency to boost WSN widespread use:Tools are needed to integrate all appropriate features for the
design of a WSNNeed for profiling and modeling of SW-HW in order to:
Identify critical featuresEvaluate/verify against application requirementsProvide design indications and suggestions
Achieve long life-cycle by componentizing SW, thus ensuring: FlexibilityExtendabilityReusability
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Desirable WSN features leading to Sustainability
Low power consumption Long operational lifetime for
battery-powered unattended WSN nodes
Joint optimization of connectivity and energy efficiency Best-effort utilization of constrained
radios in WSNs & min energy cost Self-calibration and self-healing
Recovering from failures and errors to which WSNs are prone
Efficient data aggregation Lessening the traffic load in
constrained WSNs
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Short development time Short time-to-market for
WSN systems
Programmable and reconfigurable stations Allowing for long life-cycle
development System security
Enabling protection of data and system operation
Simple installation and maintenance procedures Widespread use of WSNs
Targeting Large Scale Applications (LSK)
Despite of considerable research and important advances in WSNs, the technology for LSA is hindered by high complexity and cost
Ongoing R&D is addressing these shortcomings by focusing on energy harvesting, MW, interoperability, standardization, reliability, intelligence adaptability and scalability
For efficient WSN development, deployment, testing and maintenance, a holistic unified approach is needed to address the above WSN challenges by developing an integrated versatile platform
This platform will enable the user to evaluate and verify his development at design-time
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Holistic Approach Methodology (1)
To develop an integration tool that provides a multiple level framework of functionality composition and adaptation for a complex WSN environment consisting of:heterogeneous platform technologiesdemanding constraints
To establish a software infrastructure which couples the different views and engineering disciplines involved in the development of such a complex system, by means of: the accurate definition of all necessary rules for interconnection
of various building blocks the design of the ‘glue-logic’ which will guarantee the correctness
of the various building blocks compositions
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Holistic Approach Methodology (2)
To facilitate consistency control and evaluate the selections made by a Development Tool, and based on specific criteria provide: feedback on errors concerning consistency and compatibility warnings on potentially less optimal user selections suggestions for improving final system characteristics
To implement a planning tool that will provide answers to fundamental issues such as: the number of nodes needed to meet overall system objectives the deployment of these nodes to optimize network performance the adjustment of network topology and sensor node placement
in case of changes in data sources and network malfunctioning
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Holistic Approach Methodology - Development Flow
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Focus on core processes
Holistic Approach Methodology - Basic Entities to Attain Targets
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Middleware Level seamless connectivity and interoperability issues over widely
heterogeneous device and communication technologiesDevelopment Level
establishing a framework that encompasses components built or adapted in this endeavor and providing synthesis capabilities
evaluating system performance, in conjunction with simulation tools and HW-in-the-loop at design-time
delivering the final codeDeployment level
connectivity evaluation, critical node detection and provides techniques for links reduction
Pictorial representation of the Holistic Approach
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DesignerUser Developer DeployerField Tester
Tester
Development DeploymentWireless Sensor
NetworkMiddleware
Middleware Level Focus
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Middleware (MW)-1
Motivation:Great “programming complexity gap” between development of
WSN applications and handling of underlying system operation, in order to cope with:dynamic changes of the operational environmentdifferent user-application requirementsheterogeneityThese WSN operation specificities result to special knowledge
requirementsApplication development in most common cases turns out to be
a rather low-level programming procedure, resulting to: relatively decreased energy efficiency and QoShigh resource consumption and time-cost
Lack of a unified basis of development to handle:
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interoperability with other systems reusability of implementations
system adaptation system extendability
Middleware (MW)-2
Main Objectives:Implement a MW architecture which combines the state of the art in disjoint or loosely coupled research directions:Adoption of a uniform MDE approach which maps well through existing standard notations and SW modeling constructsUse of generalized high level application programming abstraction definitionsDeployment over a generic service/component execution framework, supporting system component reconfiguration and reprogrammingSupport of configurable resource consumption awareness both at design-time and at run-timeEnsuring interoperability based on mappings according to existing international standards and industry driven specifications
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Middleware (MW)-3
High-level Functional Abstractions: Appear on top of lower level abstractions, in order to hide
functionalities corresponding to platform and network interfaces:CPU, memory storage, radio, network stack protocols
Encapsulate functionality of system or application level components:Processing
representing application level algorithms and logic Transducer (i.e. Sensors/Actuators),
Storage and Communicationhiding underlying
heterogeneity and corresponding access mechanisms
Parameterdefining the employed
data model
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application-level abstraction
Middleware (MW)-4
Component Framework support: Combines CBD principles of accessing functionality implementations
in composing WSN systems/applications through interface contracts: IEC-61499: event-driven & data-flow process orientation SCA: typical synchronous method for call semanticsSysML covers ports representation for both event/data flow and
service-reference-properties features
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Basic MW component elements and interfaces
Function Block
Parameter
Event Value type
Interface
Property
Middleware (MW)-5
Target application development example (temperature sensing): Local node-level composition of the application:
Displays the current temperature in a local device Turns-on an alarm when the temperature exceeds a threshold
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The middleware provides the support for the function blocks interconnection
Temperature Sensing App
Timer KeyPad Custom Process Alarm
Display
Temperature Sensor
ADC
Middleware (MW)-6
Target application development example (temperature sensing): Distributed composition of the application:
Display, keypad, alarm and sensor parts exist on separate devices and exchange control and data seamlessly over the network
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Device 1
Device 2
Device 4Device 3
Temperature Sensing App
Timer
Temperature Sensor
ADC
KeyPad
Display
Custom Process
Alarm
Development Level Focus
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Development-1
Motivation:Existing development procedures of WSNs impede in some way
adequate widespread use because: In-depth knowledge is required at various levels: OSs, protocols,
platforms, programming etc.There are no fully integrated environments facilitating all phases of
development: design, develop, test, validate, maintain, extendWSN Simulation study suffers from various shortcomings:
Lack of accurate modelsUncertainties of hardware influence performance and behavior
Result: Inefficient cycles of development and unreliable system behavior estimation
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Development-2
Main Objectives: Offer useful and practical tools enhancing the following aspects of
DT for both experts and non-experts:Employ standard SW development models and methods that
correspond to final implementation architecture Increase efficiency and decrease development complexityAdopt drag-and-drop approach for component synthesis
Offer HW-in-the-Loop techniques and propose approaches that will enhance simulation-based features of prominent simulators: Increase simulation accuracyTake hardware features into considerationProvide accurate power consumption estimation
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Implementation methodology of the Development Tool
Identify key semantics from Middleware components:The MDE approach is applied, in conjunction with the Modeling
Language (SysML) for semantics description Develop a reference model (in SysML) in order to define primitive
development tool types (i.e. Function Block, Event, Parameter etc.) addressing the targeted MW architecture
Develop an application composition using the modeled primitive types
Validate the produced model by identifying errors/inconsistencies and proposing suggestions via a Synthesis Evaluation-Validation Module (SEVM)
Produce a configuration file which defines the interconnections between MW components at the implementation level and delivers the final code
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Identification of key elements comprising MW architecture
Identify all key middleware architecture elements to define a proper, well-mapped component-based synthesis model
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Property
Function Block
Value TypeEventInterface
Parameter
Function Block Event
Parameter Value Type
Interface Property
Identification of key MW elements’ relationships
Identify relationships and hierarchies between MW elementsA Function Block has one or more:
EventInputPorts and EventOutputPortsDataInputPorts and DataOutPortsActions bound with
ConditionsDataInputPort and
DataOutputPort are(= follow the structure/definition of)
ParametersEventInputPort and
EventOutputPort are EventPorts
EventPorts accept Events
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Func
tion
Bloc
kParameter
DataInputPort DataOutputPort
Action
Condition
EventOutputPortEventInputPort
EventPort
Event
Development of a SysML reference model
Componentize middleware modules as SysML reusable reference blocks Timer, Sensor, Flash and Network Protocol, FFT algorithm
The example of a Timer SysML block, describing how a simple configurable MW module timer is represented in SysML, defining: Input event ports:
“STOP”, “START”, “START_ONESHOT”, “START_PERIODIC”
Output event ports:“FIRED”
Input data ports:“BASE”, “MODE”,
“INTERVAL” Output data ports:
“NOW”4th Mediterranean Conference on Embedded Computing (MECO), June 14-18, 2015, Budva, Montenegro 25
Internal state parameters
Input data Ports
The Timer block
Output data ports
Input event ports
Input event ports
Output dEvent ports
Development of an application using the SysML model
The example of Temperature Sensing Application designed/developed using SysML blocks and interconnection constructs. The user/developer may drag n’ drop elements and draw connections between them using a well-featured Graphical User Interface (GUI) An XML file is produced (i.e. using open-source Papyrus Plug-in of Eclipse IDE)
describing blocks and interconnections4th Mediterranean Conference on Embedded Computing (MECO), June 14-18, 2015, Budva, Montenegro 26
Temperature Sensing App
Timer KeyPad Custom Process
Alarm
Display
Temperature Sensor
ADC
The produced configuration and code for the employed application’s Function Block elements (after being validated) are injected in the WSN
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SysML Development Tool
parse
.xm
l file
Mid
dlew
are
Application
FB1 FB2 FB4
FB3 FB5
Configuration chunk
FB2
FB3
FB4 FB8
FB5
FB6
FB1
FB7
FB services
Mid
dlew
are
FB3
FB5
FB7 FB8
FB2
FB4
FB1
FB6
MiddlewareOS
configchunk
WSN node
Based on the configuration MW establishes the
interconnections between the appropriate FBs
FB inter-connections indicated by the configuration file
Code chunks
Code of FBs included in the
application
FB1 code
FB1 code
FB1 code
FB1 code
Synthesis Evaluation-Validation Module (SEVM) Rationale
Validation is a crucial entity of the development process: The system synthesis described by the XML file is subjected to evaluation
and validation The meta-data that accompany the blocks in the XML file are evaluated
for consistencies against system requirements and specificationsThe consistency control ensures interoperability among different
platforms, protocols, implementations i.e. consistency of Bluetooth radio against network protocols
Evaluation of user selections regarding a particular WSN system synthesis based on criteria Feedback on errors (consistency/compatibility) Feedback on warnings (inefficiencies)
Best-Fit synthesis approach based on user requirements, letting the SEVM machine make decisions Pre-defined templates (“auto-complete” notion)
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Synthesis Evaluation-Validation Module Objectives
Component-based structure/development perfectly match SEVM Rationale Quality attributes describe the components Components can be flexibly connected Generic approach followed (independently of the level of components’
functionality)
Answered questions Given primary system quality attributes, what about the component ones? Given a set of component attributes, what about the whole system ones? Accuracy of the predicted attributes? Any special conditions and constraints? Should components concern all types of modules, from low (i.e.
communication modules) to high-level ones (i.e. application-oriented ones)?
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Comp 1 Comp 2
quality attrs quality attrs
Component LibrariesCode & metadata (xml)
Classification of typical Component Properties
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Specification/SW module Application Routing MAC
Memory (Static/Dynamic) + + +Execution Delay + + +
Operating Environment restricts + + +WSN Platform restricts + + +MAC Protocol restricts +
Communication Approach Suitability +
Synchronization + +Control Traffic Overhead + +
Routing restricts +Density-adequacy +
Mean Medium Access Delay +
High-Level Synthesis Evaluation-Validation Module (SEVM)
Application Requirements:Communication traffic
specificationsCommunication approachNode densityPacket lossReal-Time requirements
Properties of SW modules in different levels(i.e. network stack)
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Classification of Component Properties Relations
Restrictions and guidelines on user choices produce:
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Failures related to Logic and Code generation
Derived fromCompatibility checks and properties’ correlation
Memorye.g.
Delay
Warnings related to Performance degradation and Operational failures
Derived fromExcessive resource utilization (e.g. Memory)Not efficient protocol selection (e.g. Routing)
Suggestions related toPredefined SW modules compositions and Specific SW/HW components
Hardware-in-the-Loop Rationale
Integrate aspects of the a real WSN operation into dominant WSN simulation environments
Omnet++ is selected as one of the most prominent network simulator providing High modularity and flexibility Component based
architecture Various WSN oriented
frameworks focusing on different aspectsCastalia: Focusing mostly on
Physical layerMiXiM: Focusing on
Communication protocols
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OMNET++
Middleware
WSN OS HAL(i.e. TinyOS, Contiki)
Application Configuration
system call for HW-in-the-Loop
Virtual WSN
Development Tool
Real WSN
Hardware-in-the-Loop Rationale: 1st Example-Aspect
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Simulation taking into consideration real wireless transmission characteristics
Hardware-in-the-Loop Rationale: 2nd Example-Aspect
Simulation taking into consideration processing capabilities
Typical example measurements
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Application Layer
Application Layer
RoutingLayer
RoutingLayer
MACLayer
MACLayer
PHYLayer
PHYLayer
Simulated Channel
OMNET ++
Case1: All Software stack is by-passed
through HIL
Case2: Routing layer is by-passed
through HIL
RoutingLayer
MACLayer
PHYLayer
Real Mote
ApplicationLayer
RoutingLayer
MACLayer
PHYLayer
Real Mote
ApplicationLayer
Full Stack (sim)
MAC - less HIL
Full Stack HIL
Encryption HIL
Rx delay - ~1.01ms ~8.61ms ~10.46ms
Tx delay - ~0.09ms ~0.46ms ~0.47ms
end to end
delay~7.69ms ~8.7ms ~9.07ms ~10.82ms
MAC delay (sim)
~7.68ms ~7.68ms - -
Deployment Level Focus
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Deployment-1
Motivation:Deployment is a cornerstone for adequate and energy efficient WSN
performanceWSN simulation suffers from various shortcomings such as insufficient
propagation models
Main Objectives:Optimal sensing coverage of an areaRealistic representation of signal propagation considering all
environmental and HW particularitiesOptimal and energy efficient connectivityConstruction of network topology based on application-driven network
requirementsSimple installation and maintenance
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Deployment-2
Of paramount importance are the aspects of:Connectivity: seamless capability of getting data from the source
to the appropriate destinationTopology: nodes and links that allow direct communication
Objectives of a Planning Tool:Connectivity evaluation and identification of critical nodes
Critical nodes determine the reliable operation of the network, since possible malfunction or removal leads to partition
Topology controlTopology construction and link-reduction topologies
Neighbor-based link reductionRoute-related link reductionGateway association
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The parking
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Parking for >2000 cars, 500m x 150m 11 potential GW posts, 480 wireless nodes GW height: 2m, Nodes height: 0.2m Tx Power: 0dBm
Assumptions for the simulation
Parking 500m x 150m, for more than 2000 cars 11 potential GW posts: any number of GWs, up to 11, can be
selected. When the number of hops to a GW is more than 4-5 it is advisable another GW to be included to minimize the packet loss due to many number of hops
480 wireless nodes each serving 3 to 6 car-slots with magnetic or ultrasound sensors mounted on the node package or connected via wire
GW height: 2m, Nodes height: 0.2m, Tx Power: 0dBm 2-ray ground based propagation model biased with an extra
signal loss due to the presence of cars The output of the simulation is connected to Google Earth
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Connectivity evaluation and detection of critical nodes (1)
Motivation: To evaluate the connectivity, against various design
parameters such as transmitted power, link quality, number of gateways and more, and provide design guidance regarding potential network partitions
To identify network sections with high probability of being disconnected and group the nodes belonging in these partitions. Suggest the judicious placement of GWs and/or relay nodes
To evaluate the existence of critical nodes, in the case of a connected network, which can potentially cause partition
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Connectivity evaluation and detection of critical nodes (2)
Algorithms:Algebraic Graph Theory (AGT) approach:
AGT is based on representing the network topology as a graph and using linear algebra and matrix theory in studying of the graph
Depth First Search (DFS) approachDFS is an algorithm for traversing a graph from the GW of the
search tree until a node that has no children
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Connectivity evaluation and detection of critical nodes (3)
Screen shot: max Tx power 0dBm, connected
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5 GWs, 480 nodes, TxP = 0dBm Links 8844 Average number of neighbors: 17 Max hops to the GWs: 3
Connectivity evaluation and detection of critical nodes (4)
Screen shot: Tx power -10dBm, connected 23 critical nodes
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5 GWs, 480 nodes, TxP = -10dBm Links 2212 Average number of neighbors: 4 Max hops to the GWs: 10 23 critical nodes
Connectivity evaluation and detection of critical nodes (5)
Critical questions and tradeoffs to tackle: When reducing Tx power
Number of hops increase Delay increase, more effort by the nodes to contend for medium access
The number of 1-hop neighboring nodes contending for the medium decrease Decreased congestion per each hop
Delay Wise Increased Tx power leads to less number of relays but higher possibility for packet
collision and retransmission delay Packet Loss Wise
Higher number of forwarding effort by the nodes means that in each hop less congestion will be encountered but numerically higher number of access contentions must be made
Power Wise Reducing Tx power means that each hop costs less but many more hops must be
madeA nexus of highly dynamic questions relative tools could tackle
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Topology construction and link-reduction topologies (1)
Motivation:Propose reduced topology alternatives, which preserve the
connectivity and reduce the links between the nodes according to certain criteria, such as:predefined number of neighbors
Pertaining to degree of congestionspredefined n-connected topology
Pertaining to degree of robustnesspreliminary association to a gateway
Pertaining to application specific requirement
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Topology construction and link-reduction topologies (2)
Two algorithms:Algorithm 1: K-ROUTE
Use MST (Minimum Spanning Tree) algorithm and reduce the number of the communication links by creating K-route connected topologies. Only the strongest links will be part of the new topology
Algorithm 2: N-NEIGHBThe algorithm is based on the idea to ensure N-number of
neighbors, thus providing a handle on the degree of contention
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Topology construction and link-reduction topologies (3)
Screen shot: K-Route, 4-route
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5 GWs, 480 nodes, TxP = 0dBm Links 3872 Average number of neighbors: 7 Max hops to the GWs: 7
Screen shot: N-NEIGHB, 6 neighbors
Topology construction and link-reduction topologies (4)
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5 GWs, 480 nodes, TxP = 0dBm Links 3396 Average number of neighbors: 6 Max hops to the GWs: 7
Gateway association (1)
Motivation:To associate the nodes to the closest GWs to ensure 1 hop
direct communication when possible, at a Tx power of 0 dBmTo select, if 1-hop communication is possible to more than one
GW, the one with the better RSS linkWhen 1-hop direct communication is not possible, to evaluate
the multi-hop connection, based on the weight of the link, and associate the node with the GW, providing better overall link weight
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Screen shot 1: after the association to 5 GWs
Gateway association (2)
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5 GWs, 480 nodes, TxP = 0dBm Max hops to the GW: 3
Screen shot 2: after the association to 3 GWs
Gateway association (3)
4th Mediterranean Conference on Embedded Computing (MECO), June 14-18, 2015, Budva, Montenegro 52
3 GWs, 480 nodes, TxP = 0dBm Max hops to the GW: 7
Thank you for your attention
George Papadopoulos, Professor EmeritusIndustrial Systems Institute, RIC “ATHENA”, Patras
Applied Electronics Laboratory, ECE Dept., University of [email protected]
http://www.apel.ece.upatras.gr/papadopoulosTel.: 0030-2610-996423
Acknowledgement:ARTEMIS Joint Undertaking Project no 269389 WSN-DPCM
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