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Operating Systems for Wireless Sensor Networks in Space. Abdul-Halim Jallad and Tanya Vladimirova. Outline of Presentation. Applications of wireless sensor networks in space Formation flying missions overview Requirements analysis of operating systems for formation flying missions - PowerPoint PPT Presentation
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Abdul-Halim Jallad,Tanya Vladimirova Page 1 MAPLD 2005/1005
Operating Systems for Wireless Sensor Networks
in Space
Abdul-Halim Jallad andTanya Vladimirova
Abdul-Halim Jallad,Tanya Vladimirova Page 2
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Outline of Presentation Applications of wireless sensor networks
in space Formation flying missions overview Requirements analysis of operating
systems for formation flying missions Testbed development Conclusions
Abdul-Halim Jallad,Tanya Vladimirova Page 3
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Wireless Sensor Networks: Convergence of Technologies
Sensors: Miniaturization and micromachining makes tiny and low-cost sensors available commercially
Embedded computing: Small and low-cost processors that are networked together facilitate collaboration through information and resource sharing
Wireless communications: optical and RF communications enable networking between nodes
Wireless sensor
networks
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Wireless Sensor Networks in Space
1) Manned Spacecraft missions: e.g. crew health monitoring
Temperature Sensors 3)
Spacecraft Diagnostics and monitoring
4) Inter-planetary Exploration
Figure from http://sensorwebs.jpl.nasa.gov/
2) Spaced-based formation flying wireless sensor networks
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Multi-Satellite Missions: Terminology
A Virtual Satellite is a spatially distributed network of individual satellites collaborating as a single functional unit, and exhibiting a common system-wide capability to accomplish a shared objective.
A Distributed Space System (DSS) is a system that consists of two or more satellites that are distributed in space and form a cooperative infrastructure for science measurement data acquisition, processing analysis and distribution.
A Sensor Web is a system of intra-communicating spatially distributed sensor crafts that may be deployed to monitor environments. Sensor webs may involve many non-space elements and are therefore not completely covered by DSS.
A Constellation is a group of satellites that have coordinated coverage, operating together under shared control, synchronised so that they overlap well in coverage and reinforce rather than interfere with other satellites' coverage.
A Cluster is a functional grouping of spacecraft, formations, or virtual satellites.
A Formation is a multiple-spacecraft system with desired position and/or orientation relative to each other or to a common target. Formation flying is the term used for the tracking and maintenance of a desired relative separation, orientation or position between or among spacecraft.
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Formation-Flying Missions:Types
Signal Separation: Measurements from the same source are collected by spatially distributed sensors on-board different nodes in the formation e.g. large synthetic apertures.
Signal Combination: Distinct sensors on separate nodes collect data from different sources and merge this data on-board of the formation to extract global information of a particular phenomenon e.g. Earth observation-1 mission.
Signal Coverage: A Sensor Web with identical sensors on the nodes with the purpose of covering wide areas of surface (e.g. multi-point sensing).
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Formation-Flying Missions: The Information System
Formation-Flying
Missions:Information
System
Sensors and Actuators: These may be divided into three classes – spacecraft specific, formation-flying specific and payload specific
On-Board Computing:• Hardware is to be power and memory efficient while being fault-tolerant.• Software includes:
– mission software – middleware– an operating system to support distributed services.
Inter Satellite Communications:Intersatellite links are different from terrestrial WSN wireless links in two main aspects: • large distances involved and• predictability
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Model Application
To investigate the advantages and disadvantages of distributed computing on-board of formation-flying (FF) missions
To study possible implementations of distributed computing on-board FF missions
To propose an optimal operating system architecture for such missions
For the purpose of narrowing down the scope of this investigation we focus on a particular type of FF missions – virtual satellites
Application: Sensor web: Imaging Signal Separation:
Synthetic apertures The satellite nodes:
Mass <= 1 Kg Area <= 1 cm3 Power <= 2 Watts Orbit = Low Earth
Orbit (LEO) ~ 600Km
Mission ModelAims of Research
The Network Separation distances
= in the order of kilometers
Use of directional antennas.
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Formation-Flying Mission: Information System Architecture
System
Threads
Address space
Files
Hardware Drivers
Physical
Data Link
Network
Transport
Sensor Driver
Hardware Sensor
Middleware management
Algorithms Modules Services Virtual Machine
App1 App2 App3
P o w er
M a n a g e m e nt
Application
Hardware
Middleware
Operating System
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OS Design for Formation-Flying Missions
Process description and control:
Fault-tolerance: e.g. process replication
Memory considerations Concurrency:
FF missions are distributed systems and involve concurrency
Memory management: Use of bulk memory Program memory wash
Input/output management File management:
Fault-tolerance Networking:
Space protocol for ISL and ground space links
Security Scheduling:
Real-Time scheduling Low-power scheduling
Process Descriptionand Control
Concurrency
Networking
FileManagement
Security
Input/OutputManagement
Scheduling
MemoryManagement
Main Functions:
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OS Design Factors for Formation-Flying Missions
OBDH The architecture of the on-board
data handling system (e.g. distributed, centralized, multi-processor etc.) affect the operating system design
ISL The OS needs to consider the
bandwidth, power consumption and unreliability of the inter-satellite links while making distributed decisions
Formation Flying (FF) The effect of the relative
dynamics brought by FF on the OS design needs to be investigated
On-board Software The nature of the applications
running on-board and its distribution among the FF nodes may have a direct impact on the OS design
Constraints The limited size and therefore
available energy for computation and communication is an important factor that the OS design has to consider
Factors
OperatingSystem
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On-Board Data Handling for Pico-Satellites
OBDH
Ultra-lowPower Advanced
Packaging
Reconfigurablehardware
SOC*
ASICsFPGAs
SiGe onSOI
* = system-on-a-chip: may involve various technologiesincluding mixed-signals (analog/digital) on a single substrate
Multi-processor Systems
Time-Scale = ???
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Types of Operating Systems
Operating System
Description Pros Cons Example/ Mission
Monolithic Almost any procedure can call any other procedure.
Efficient Lack modularity
OS: LinuxMission: None
Microkernel (client/server)
A few essential functions are embedded in the kernel. Other services run as processes in user mode.
• Flexible• Well suited for distributed systems
Less efficient than monolithic
OS: QNX, VxWorksMissions: TiungSAT-1, PROBA
Virtual Machines
Exact copy of bare hardware.
Portable Low-performance
OS: Embedded Java Virtual machineMission: None
Component-Based
The Operating system consists of a set of independent components representing system resources
• Portable• Efficient• Well suited for distributed systems
OS: TinyOSMission: None
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The TinyOS: Component-Based OS
Operating system specifically designed for wireless sensor networks
Applications consist of scheduler and a graph of components
• “Higher-level” components issue commands to and respond to events from “Lower-level” components
• Components contain: Set of command handlers, Set of event handlers, A fixed size storage frame, Collection of simple threads which can be scheduled.
TinyOS TinyOS Component
Components can be implemented in hardware or software.
Events propagate upward in the hierarchy
Commands propagate downward in the hierarchy.
TinyOS Application
FrameTasks
Commands received
Events received
Events initiated
Commands made
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Operating System Design for Swarms of Pico-Satellites
Fault tolerance Small foot-print Low-power consumption Support for reconfigurable
computing. Distributed system support
Scalability Support for inter-satellite
link communications
Thread-based model
Event-based model
Conclusion: The component-based structural model provides flexibility, reusability and is suitable for distributed systems design while the event-based behavioural model provides speed, low power and memory efficiency.
Design Requirements
Component-Based Model
Execution-Model
Component library
-Tasks perform computations
-Tasks are implemented as finite state machines
- States of tasks are transitioned through events
-The system uses a main thread, which hands off tasks to individual task-handling threads
-High context switch overhead
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Distributed Computing for Formation-Flying Missions: Testbed
GR-PCI-XC2V-FT
LEON-3 Multiprocessor OBC
XSV800
LEON-3 Multiprocessor OBC
XSV800
LEON-3 Multiprocessor OBC
Ethernet
Windows XP PC
STK Matlab
SimulinkSatellite
Tool Kit
TCP/IP server
STK Advanced
AO
STK/ Connect
Linux development platform
DSU MonitorDDD
GCCCompiler
Programming Environment
RS232
Visualization
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System Emulation
GR-PCI-XC2V-FT XC2V3000 Virtex-II
FPGA Ethernet PHY interface LEON-FT core Support On-board memory
SRAM SDRAM Flash PROM
Figure from the “LEON-PCI-XC2V Development board user manual”
XSV800 XCV800 Virtex
FPGA Ethernet PHY
interface On-board
memory SRAM Flash Prom
Figure from the www.xess.com website
Mica2 motes 916MHz Multi-
channel Radio Transceiver
ATMEL128L 8-bit low-power processor
Compatible with TinyOS (specifically designed for sensor networks).
Node Emulation HardwareDistributed System Emulation Hardware
Figures from mica2 datasheet
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Pico-Satellite Computing Platform
The chosen processor is the LEON-3 soft IP core
32-bit SPARC V 8 architecture
Could be used in a multi-processor system
Soft core (suitable for developing system-on-chip prototypes)
Power-down mode is supported
Embedded Hardware Debug Support Unit (DSU).
LEON-3 in a multi-prosessor configuration
Figure from www.gaisler.com
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Conclusions Wireless sensor networks are a promising technology for space applications
including orbital formation-flying (FF) missions and inter-planetary exploration.
This research focuses on implementation of distributed computing on-board FF missions employing the wireless sensor networks concept.
The various factors that affect the operating system (OS) design of FF missions may be divided into two categories:
Traditional OS requirements: e.g. code efficiency and real-time performance. Specific requirements for FF missions: e.g. fault-tolerant distributed computing,
orbit dynamics etc. A novel OS for multi-satellite FF missions should have the following features:
An event-based execution model allowing to achieve low-power consumption and to fulfil the concurrency requirement with minimal amount of code.
A component-based structural model allowing to achieve the modularity requirement and enabling the hardware/software boundary crossing, which provides support for reconfigurable and distributed computing.
The TinyOS is selected as the baseline OS to be studied and adapted for use in distributed FF satellite missions.