A Process Oriented Development Flow for Wireless System Networks by Bernard Pottier

A Process Oriented Development Flow for Wireless Sensor Networks Bernard Pottier*, Guillaume Kremer & Jimmy Osmont Université de Brest * LabSTICC, UMR CNRS 3192

WSN and applications
W ireless S e nsor N etworks (WSN) are an expanding application field
Green technology : environment, process control, power saving
Human friendly : assists decisions in number of situations
Driven by progresses in communications, integration technologies
Application examples
Parking in San Francisco: 6000 sensors connected to GPS/GSM service reduce car traffic and pollution,
Forest fire detection from mesh connected sensors powered from imbalance in pH between tree and soil (MIT),
Services for disabled persons/ bus transportation.
Farming : cattle, green house, fields monitoring.

Our objectives
To support WSN design as a top-down flow:
Sensor physical distribution and connectivity
Communication layer management
Application level algorithm design
Code generation for sensors
2 stages flow
Abstract design ,simulation
Code synthesis
Developped in Smalltalk-80

WSN components
Sensors
Execution is a loop including
Communications
Local interaction with control and acquisition devices
Low power, when possible local power source, low cost
Practical example
PsoC (Mixed analogue/logic reconfigurable system on chip)
Spread spectrum wireless transceiver (10s to 100s meters)
Temperature, pressure, presence, light, buzzer, ..
Power

WSN organizations
Static
Star network, hub to internet (green house)
Mesh connected with routing and gateways (SF parking, forest)
Dynamic
Mobile fleet (roaming cattle)
Mobile in static or fleet (shepherd collecting information on sheep, bus exchanging information together / with bus stop

An evident challenge is distributed algorithms
Static deployment problems
Network connectivity, fault tolerance, adaptive routing, control flow, memory/buffer use,
Control, data collection, dynamic code distribution
Communication scheduling ( idle to bandwidth saturation)
Dynamic behaviour problems
Routing algorithms, managing identities,
Data storing and collection

A Framework for WSN Modelling and Synthesis
Uses a two stage flow:
Behaviour level (design):
Modelling network topologies as communicating processes.
Local interactions (sensing, controlling)
Local contribution to distributed behaviour
Tuning and optimizing design and algorithms from simulations
Synthesis level (implementation)
Dimensioning node characteristics from stage 1 parameters
Target isolation
Native code production, or virtual machine for stage 1 intermediate code.

WSN abstract model
NetworkGraph
Collection of nodes
NetworkNode
NodeName (process name)
Input Link collection
Output Link collection
Program/Procedure Name
Link
Source node
Destination node
Algorithms, builders, generators

Syntax based builder
Smalltalk 'methods' described using VW ParserCompiler
methodName messages alphabet … . NodeName1 { destNodes1 … } ProgramNode NodeName2 { destNodes2 … } ProgramNode
Network is developped from a browser

Random topologies builder
Generate a sensor distribution on a surface
Surface known as a rectangle
Sensor wireless neighborhood known as a reachable distance
Arbitrary number of sensors
Compute the connectivity between nodes
Build a corresponding network, drawing, text.

Physical deployment builder
Flow
Read a map, a photo
Define scales for this background
Define sensor transmit distance
Place sensors and build a network.
Computes network on the fly.
Sandbox for the deployment of a sensor network along bus lines and bus stop

Generators
Graphviz (.dot file)
Occam program:
Concurrent organization : process skeleton, channel declaration,
Process skeleton for a synchronous cycle

Occam Generator
Hundred of processes, thousands of channels
Fixed behaviour for the synchronous model :
Setup an initial state, prepare initial message output
Loop forever
Send messages on output links
Receive messages on input links
Change the node state according to current state and input messages
Prepare next message output
(c and d) place holders for programmer.

Synchronous model : Why?
Sensor networks are synchronous:
Sharing a reference clock
Sensors schedule listening and emitting interleaved with silences
Time division, frequency or channel division
Large number of known algorithms:
Retrieving network characteristics – diameter – spanning trees
Distributed reduction operations, broadcasts
Routing with table exchanges, dynamic routing for mobiles
Can be implemented on top of Occam:
Concurrent send and receive operations avoid deadlocks
Simulation of very large networks in native code for multi-cores

Generator Status
Very large process networks generate, compile and execute on multiprocessor
Significant set of algorithms implemented: routing, naming, flow control.

Generator evolutions: VM
Use of Occam intermediate bytecodes (TIS) to program sensors
Virtual machine to execute TIS subset for synchronous model
Channels operations are replaced by scheduled wireless exchanges (TDMA)
Several bytecodes for parallel constructs, loops, operations implemented
Stage 2 Stage 1

Flow alternatives
Use of Smalltalk to describe synchronous behaviour
Methods export blocks for setup and transition
Blocks operate on method temporary variables
A process system is generated with communications operated using SharedQueues
Translations similar to TIS
Stage 1 (ST80 subset) Stage 2

Project Status
Emerging project
Appears as a contribution to PuceCom regional project in Brittany
Cooperation developing with NUST in Pakistan
Contributions of UBO students
Hardware targets : Cypress PsoC and RF circuits, ARM7, GPS, …
Contacts with industry : urban transportation, GIS, …
VisualWorks NC, KroC (Occam), store 'students' @ as.univ-brest.fr
Wish to contribute to sustainable development
( Oyster-catchers at round-island, bay of Brest )

A Process Oriented Development Flow for Wireless System Networks by Bernard Pottier

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