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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

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operating systems for wireless sensor networks in space

Operating Systems for Wireless Sensor Networks in Space

Abdul-Halim Jallad and

Tanya Vladimirova

outline of presentation
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
wireless sensor networks convergence of technologies
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

Sensors: Miniaturization and micromachining makes tiny and low-cost sensors available commercially

Wireless

sensor

networks

wireless sensor networks in space

2) Spaced-based formation flying wireless sensor networks

3) Spacecraft Diagnostics and monitoring

Temperature Sensors

Wireless Sensor Networks in Space

1) Manned Spacecraft missions: e.g. crew health monitoring

4) Inter-planetary Exploration

Figure from http://sensorwebs.jpl.nasa.gov/

multi satellite missions terminology
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 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 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 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.
formation flying missions types
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.

  • 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).

  • 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.

formation flying missions the information system
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.
  • Inter Satellite Communications:
  • Intersatellite links are different from terrestrial WSN wireless links in two main aspects:
  • large distances involved and
  • predictability

Formation-

Flying

Missions:

Information

System

model application
Model Application

Mission Model

The Network

Aims of Research

  • 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
  • Separation distances = in the order of kilometers
  • Use of directional antennas.
formation flying mission information system architecture
Formation-Flying Mission: Information System Architecture

Application

App1

App2

App3

Power

Management

Algorithms

Modules

Services

Virtual Machine

Middleware

Middleware management

System

Threads

Address space

Files

Transport

Operating System

Network

Data Link

Physical

Hardware Drivers

Sensor Driver

Hardware

Hardware

Sensor

os design for formation flying missions
OS Design for Formation-Flying Missions

Main Functions:

Process Description

and Control

  • 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

Scheduling

Concurrency

Memory

Management

Input/Output

Management

File

Management

Networking

Security

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

OS Design Factors for Formation-Flying Missions

Factors

Operating

System

on board data handling for pico satellites

Time-Scale = ???

On-Board Data Handling for Pico-Satellites

OBDH

* = system-on-a-chip: may involve various technologies

including mixed-signals (analog/digital) on a single substrate

Ultra-low

Power

SOC*

Reconfigurable

hardware

Advanced

Packaging

Multi-processor

Systems

SiGe on

SOI

FPGAs

ASICs

the tinyos component based os

Commands received

Events initiated

Tasks

Frame

Commands made

Events received

The TinyOS: Component-Based OS

TinyOS

TinyOS Component

TinyOS Application

  • 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.

Components can be implemented in hardware or software.

Events propagate upward in the hierarchy

Commands propagate downward in the hierarchy.

operating system design for swarms of pico satellites
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

Design Requirements

Component-Based Model

Execution-Model

Thread-based model

Event-based model

Component library

  • The system uses a main thread, which hands off tasks to individual task-handling threads
  • High context switch overhead
  • Tasks perform computations
  • 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 event-based behavioural model provides speed, low power and memory efficiency.

distributed computing for formation flying missions testbed
Distributed Computing for Formation-Flying Missions: Testbed

Windows XP PC

Visualization

STK

Matlab

STK Advanced AO

Satellite Tool Kit

TCP/IP server

Simulink

STK/ Connect

Ethernet

GR-PCI-XC2V-FT

XSV800

XSV800

LEON-3 Multiprocessor OBC

LEON-3 Multiprocessor OBC

LEON-3 Multiprocessor OBC

RS232

Linux development platform

DDD

GCC

Compiler

Programming Environment

DSU Monitor

system emulation
GR-PCI-XC2V-FT

XC2V3000 Virtex-II FPGA

Ethernet PHY interface

LEON-FT core Support

On-board memory

SRAM

SDRAM

Flash PROM

System Emulation

Distributed System Emulation Hardware

Node Emulation Hardware

  • XSV800
    • XCV800 Virtex FPGA
    • Ethernet PHY interface
    • On-board memory
      • SRAM
      • Flash Prom
  • Mica2 motes
    • 916MHz Multi-channel Radio Transceiver
    • ATMEL128L 8-bit low-power processor
    • Compatible with TinyOS (specifically designed for sensor networks).

Figure from the “LEON-PCI-XC2V Development board user manual”

Figure from the www.xess.com website

Figures from mica2 datasheet

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).

Pico-Satellite Computing Platform

LEON-3 in a multi-prosessor configurationFigure from www.gaisler.com

conclusions
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.