abdul-halim jallad, tanya vladimirova page 1 mapld 2005/1005 operating systems for wireless sensor...

Abdul-Halim Jallad,Tanya Vladimirova MAPLD 2005/1005

Operating Systems for Wireless Sensor Networks

in Space

Abdul-Halim Jallad andTanya Vladimirova

Abdul-Halim Jallad,Tanya Vladimirova

MAPLD 2005/1005

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


MAPLD 2005/1005

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


MAPLD 2005/1005

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


MAPLD 2005/1005

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.


MAPLD 2005/1005

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).


MAPLD 2005/1005

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


MAPLD 2005/1005

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.


MAPLD 2005/1005

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


MAPLD 2005/1005

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:


MAPLD 2005/1005

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


MAPLD 2005/1005

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 = ???


MAPLD 2005/1005

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


MAPLD 2005/1005

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


MAPLD 2005/1005

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


MAPLD 2005/1005

Distributed Computing for Formation-Flying Missions: Testbed

GR-PCI-XC2V-FT

LEON-3 Multiprocessor OBC

XSV800


XSV800


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


MAPLD 2005/1005

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


MAPLD 2005/1005

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


MAPLD 2005/1005

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.

abdul-halim jallad, tanya vladimirova page 1 mapld 2005/1005 operating systems for wireless sensor...

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