Transcript 1005_jallad_p

Operating Systems
for Wireless Sensor Networks
in Space
Abdul-Halim Jallad and
Tanya Vladimirova
Abdul-Halim Jallad,
Tanya Vladimirova
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Outline of Presentation
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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
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Wireless Sensor Networks:
Convergence of Technologies
Wireless communications: optical
and RF communications enable
networking between nodes
Embedded computing:
Small and low-cost
processors that are
networked together
facilitate collaboration
through information
and resource sharing
Abdul-Halim Jallad,
Tanya Vladimirova
Wireless
sensor
networks
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Sensors:
Miniaturization and
micromachining
makes tiny and lowcost sensors
available
commercially
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Wireless Sensor Networks
in Space
1) Manned
Spacecraft
missions: e.g.
crew health
monitoring
3) Spacecraft
Diagnostics
and
monitoring
Abdul-Halim Jallad,
Tanya Vladimirova
2) Spaced-based
formation flying
wireless sensor
networks
4) Inter-planetary
Exploration
Temperature
Sensors
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Figure
from
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http://sensorwebs.jpl.nasa.gov/
Multi-Satellite Missions:
Terminology
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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 Cluster is a functional
grouping of spacecraft,
formations, or virtual
satellites.
A Sensor Web is a system of intracommunicating 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.
Abdul-Halim Jallad,
Tanya Vladimirova
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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.
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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 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 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.
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Signal Separation:
Measurements from the
same source are
collected by spatially
distributed sensors onboard different nodes in
the formation e.g. large
synthetic apertures.
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Abdul-Halim Jallad,
Tanya Vladimirova
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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
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.
Abdul-Halim Jallad,
Tanya Vladimirova
Inter Satellite
Communications:
FormationFlying
Missions:
Information
System
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Intersatellite links are
different from terrestrial
WSN wireless links in
two main aspects:
• large distances
involved and
• predictability
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Model Application
Mission Model
Aims of Research
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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
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For the purpose of
narrowing down the scope
of this investigation we
focus on a particular type
of FF missions – virtual
satellites
Application:
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Separation distances =
in the order of
kilometers
Use of directional
antennas.
Sensor web: Imaging
Signal Separation:
Synthetic apertures
The satellite nodes:
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Abdul-Halim Jallad,
Tanya Vladimirova
The Network
Mass <= 1 Kg
Area <= 1 cm3
Power <= 2 Watts
Orbit = Low Earth Orbit
(LEO) ~ 600Km
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Formation-Flying Mission:
Information System Architecture
Application
Middleware
App1
Algorithms
App2
Modules
App3
Services
Virtual Machine
P
o
w
er
Middleware management
Operating
System
System
Transport
Threads
Network
Address space
Data Link
Physical
Files
Hardware
Hardware Drivers
Sensor Driver
Hardware
Abdul-Halim Jallad,
Tanya Vladimirova
M
a
n
a
g
e
m
e
nt
Sensor
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OS Design for
Formation-Flying Missions
Main Functions:
Process Description
and Control
Scheduling
Memory
Management
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Concurrency
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Input/Output
Management
File
Management
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Security
Networking
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Tanya Vladimirova
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Process description and
control:
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Fault-tolerance: e.g.
process replication
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Memory considerations
Concurrency:
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FF missions are
distributed systems and
involve concurrency
Memory management:
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Use of bulk memory
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Program memory wash
Input/output management
File management:
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Fault-tolerance
Networking:
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Space protocol for ISL
and ground space links
Security
Scheduling:
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Real-Time scheduling
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Low-power
scheduling
OS Design Factors for
Formation-Flying Missions
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OBDH
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ISL
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Operating
System
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The effect of the relative dynamics
brought by FF on the OS design
needs to be investigated
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
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Abdul-Halim Jallad,
Tanya Vladimirova
The OS needs to consider the
bandwidth, power consumption
and unreliability of the intersatellite links while making
distributed decisions
On-board Software
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The architecture of the on-board
data handling system (e.g.
distributed, centralized, multiprocessor etc.) affect the operating
system design
Formation Flying (FF)
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Factors
The limited size and therefore
available energy for computation
and communication is an important
factor that the OS
design
has to
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consider
On-Board Data Handling
for Pico-Satellites
* = system-on-a-chip:
may involve various
technologies
including mixed-signals
(analog/digital) on a
single substrate
OBDH
Ultra-low
Power
Advanced
Packaging
Reconfigurable
hardware
Multi-processor
Systems
SOC*
SiGe on
SOI
FPGAs
ASICs
Time-Scale = ???
Abdul-Halim Jallad,
Tanya Vladimirova
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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: Linux
Mission: 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, VxWorks
Missions:
Virtual
Machines
Exact copy of bare hardware.
Portable
Lowperformance
OS: Embedded Java
ComponentBased
The Operating system consists
of a set of independent
components representing
system resources
Abdul-Halim Jallad,
Tanya Vladimirova
•
Portable
• Efficient
• Well suited for
distributed systems
•
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TiungSAT-1, PROBA
Virtual machine
Mission: None
OS: TinyOS
Mission: None
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The TinyOS:
Component-Based OS
TinyOS
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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.
Abdul-Halim Jallad,
Tanya Vladimirova
TinyOS Component
Commands
received
Tasks
Commands
made
TinyOS
Application
Events
initiated
Frame
Events
received
Components can be
implemented in
hardware or software.
Events propagate
upward in the hierarchy
Commands propagate
downward in the
hierarchy.
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Operating System Design
for Swarms of Pico-Satellites
Design Requirements
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Fault tolerance
Small foot-print
Low-power consumption
Support for reconfigurable
computing.
Distributed system support
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ComponentBased Model
Component
library
Scalability
Execution-Model
Thread-based
model
Event-based
model
-The system uses
a main thread,
which hands off
tasks to
individual taskhandling threads
-Tasks perform
computations
-High context
switch overhead
Support for inter-satellite
link communications
-Tasks are
implemented as
finite state
machines
- States of tasks
are transitioned
through events
Conclusion: The component-based structural model provides flexibility,
reusability and is suitable for distributed systems design while the eventbased behavioural model provides speed, low power and memory efficiency.
Abdul-Halim Jallad,
Tanya Vladimirova
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Distributed Computing for
Formation-Flying Missions: Testbed
Windows XP PC
Visualization
STK
Matlab
STK
Advanced
AO
Satellite
Tool
Kit
STK/
Connect
TCP/IP
server
Simulink
Ethernet
GR-PCI-XC2V-FT
XSV800
LEON-3
Multiprocessor OBC
XSV800
LEON-3
Multiprocessor OBC
LEON-3
Multiprocessor OBC
RS232
Linux development platform
Programming
Environment
Abdul-Halim Jallad,
Tanya Vladimirova
DDD
GCC
Compiler
DSU Monitor
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System Emulation
Distributed System
Emulation Hardware
Node Emulation Hardware
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GR-PCI-XC2V-FT
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XC2V3000 Virtex-II FPGA
Ethernet PHY interface
LEON-FT core Support
On-board memory
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SRAM
SDRAM
Flash PROM
Figure from the “LEON-PCI-XC2V Development
board user manual”
Abdul-Halim Jallad,
Tanya Vladimirova
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XSV800
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XCV800 Virtex
FPGA
Ethernet PHY
interface
On-board memory
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SRAM
Flash Prom
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Mica2 motes
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916MHz Multichannel Radio
Transceiver
ATMEL128L 8-bit
low-power
processor
Compatible with
TinyOS (specifically
designed for
sensor networks).
Figure from the www.xess.com website
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Figures from mica2 datasheet
Pico-Satellite Computing
Platform
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The chosen processor is the
LEON-3 soft IP core
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32-bit SPARC V 8
architecture
Could be used in a multiprocessor system
Soft core (suitable for
developing system-on-chip
prototypes)
Power-down mode is
supported
Embedded Hardware Debug
Support Unit (DSU).
Abdul-Halim Jallad,
Tanya Vladimirova
LEON-3 in a multi-prosessor
configuration
Figure from www.gaisler.com
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Conclusions
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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:
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A novel OS for multi-satellite FF missions should have the following features:
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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.
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.
Abdul-Halim Jallad,
Tanya Vladimirova
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