Docstoc

Slide 1 - Polar Radar for Ice Sheet Measurements

Document Sample
Slide 1 - Polar Radar for Ice Sheet Measurements Powered By Docstoc
					    Multi-Link Iridium Satellite Data
Communication System for Polar Research


             Abdul Jabbar Mohammad
               (September 15, 2005)




                                University of Kansas
Motivation - PRISM
Polar Radar for Ice Sheet Measurements (PRISM)
    Field experiments in Greenland and Antarctica
    Data telemetry from the field to the University
         Science data
    Access to University and web resources from field
         Internet, email
         ssh, file transfer
    Public outreach
         Involvement of student community (K-12) in scientific research
         Virtual experience of the polar expedition for the science community
    Lack of conventional communication facilities
         Satellite communication is the only viable solution


                                                                                 2
                                                   University of Kansas
    Satellite Data Communication
    Commercial Satellite systems
         No coverage or intermittent coverage
         Prohibitively expensive ($3 - $30 per
          MB)


    Special Purpose Satellite
     systems                                            Inmarsat
         ATS3, LES9, GOES, TDRS 1,and
          MARISAT2
         Broadband Access
         Geo-synchronous : Limited visibility
          (10-13 hrs/day)
         Low elevation angles : extremely large
          ground terminals
                                                        Globalstar
                                                                          3
                                                   University of Kansas
    Iridium Satellite System
    Low earth orbiting satellite system
         True pole-to-pole coverage
         66 Satellites in orbit
         Altitude of 780 Km
         Minimum elevation angle – 8.2 0
         Average satellite view time – 10 minutes
         Access Scheme – FDMA and TDMA
         Maximum number of users – 80 users per a diameter of 318 Km
         Low cost availability for research purposes ( NSF sponsored)

    Data communication features
         Type of data services – Iridium-to-PSTN, Iridium-to-Iridium
         Throughput – 2.4 Kbps, primarily intended as a voice only system
         Cannot support most of the data communication requirements of polar research
         Not practical to be used as a main stream/ life-line communication system

                                                                                         4
                                                              University of Kansas
Iridium Based Data Communication
Idea – Combine multiple Iridium channels in to a single logical link

Inverse Multiplexing

   Distributes data from a single application over multiple links.

   Increases the available bandwidth per application

   Packet based inverse multiplexing solutions exist - Multi-link point-to-point
    protocol (MLPPP)


                                                                   Low Bandwidth Links
      App 1
                       High Bandwidth Link




                                                         Inv-Mux
                 Mux




      App 2                                    App 1

      App 3

                Multiplexing
                                                           Inverse multiplexing

                                                                                         5
                                                       University of Kansas
Multi-channel Iridium System – Protocol Stack
  Remote System                                         Local System

     Application                                           Application


   HTTP, FTP, SSH                                       HTTP, FTP, SSH


        TCP                                                   TCP


         IP                                                    IP


     PPP/MLPPP       point-to-point satellite links       PPP/MLPPP


   Physical Modems                                      Physical Modems


                                                                          6
                                               University of Kansas
    4-Channel Iridium System - Design

       Remote                         I. Modem 1

                      USB-SERIAL




                                                                Antenna
       System                         I. Modem 2                                            Iridium




                                                                  Grid
                                      I. Modem 3                                           Gateway
      PPP client                      I. Modem 4

                   Remote Subsystem




                                                   Multi-port
                                                   PCI card
                                    Local
                                                                          Modem
                                   System                                                   PSTN
                                                                           Pool
                      PPP Server
                                        Local Subsystem


    4 Iridium – 4 PSTN data configuration
    Discrete components
    Patch antennas
    Control software on a rugged Laptop
                                                                                                         7
                                                                                  University of Kansas
4-Channel Iridium System            Testing at NGRIP, Greenland-2003




4-Channel Iridium System at NGRIP       Antenna setup at NGRIP



                                                                       8
                                        University of Kansas
    4-Channel Iridium System -2003 Conclusions

    Reliable console based management software

    End-to-end network worked

    4-channel throughput = 9.26 Kbps; System efficiency > 90%.

    Average time interval between call drops = 100 minutes

    Average up-time ~ 90%

    Average round trip time with Iridium-PSTN configuration ~ 2 seconds

    Problems with USB-Serial converter in Linux

    PPP level compression was resulting in corrupted modem termination – loss of packets

    Primary modem failure resulted in the termination of all the other modems

    Not fully autonomous


                                                                                            9
                                                              University of Kansas
    4-Channel Iridium System -2003 Conclusions

    Identified areas for additional research
         Increase the bandwidth - Scale the system from 4-channels to 8-
          Channels

         Reduce delay – use Iridium-to-Iridium configuration in data-after-voice
          (DAV) modem

         Improve management and Control - more structured system

         Solve the primary modem drop problem

         Develop a plug and play integrated system

         Improve the user friendliness of the system

         Reduce the antenna footprint



                                                                                    10
                                                        University of Kansas
8-channel Iridium System – Design Elements
   8 channel Iridium-to-Iridium configuration
   On-board computer to run the control software
   GUI based management/control software
        Allows on-field reconfiguration in different data modes:
              a) Iridium-Iridium DAV mode,
              b) Iridium-Iridium data mode,
              c) Iridium-PSTN mode
        System parameter tuning
        Status monitoring

   Inverted cone antennas - easily mounted on field and do not need a
    external ground plane.
   Integrated field unit – plug and play

                                                                                    11
                                                             University of Kansas
    8-channel Iridium System – Integrated Unit
                 Bottom View                       Top View




                                        19”




                      24”                     Front View

    Dimension         : 9x19x24 inch
    Weight            : 50 lbs
    Operating temp    : -30 to 60 c                                 9”
    Power input       : 120 V AC
    Replication Costs : ~$18,000

                                                                      12
                                              University of Kansas
8-channel Iridium System – Client Software
                       Client Software consists of three modules:


                         Graphical User Interface
                            Easy Configuration and Operation
                            Does not require experienced users

                         Control Software

                            It is the core of the software
                            Automatic Modem Control

                         XML Database
                            Registers all call drops and retrials

                            Makes it possible for future analysis of
                             network performance data



                                                                     13
                                University of Kansas
8-channel Iridium System – Client GUI




                                                   14
                            University of Kansas
8-channel Iridium System – Client GUI




                                                   15
                            University of Kansas
 8-channel Iridium System –Network Architecture

               World Wide Web                                                   Polar Camp,
                                                                                Greenland/Antarctica
                                                                                                                            100 Mbps
                                                                                                                            Ethernet
                                 (Default gateway)                                  (Default gateway)            user 4
                                     PPP Server                                        PPP Client
     ITTC Default
     Router
                                                      P-T-P Satellite link
                          eth0                 ppp0                          ppp0                eth0



      User 2
                     100 Mbps         User 1
                     Ethernet                                                                           user 3

                     User 3


                                                                                Camp                    user 2
                                                                                WI-FI                                     user 1


ITTC Network, University of Kansas

                                                                                                                                   16
                                                                                      University of Kansas
Field Experiments – System Implementation




                        8-Channel system in a weather-port at
                        SUMMIT camp in Greenland, July 2004




                                                            17
                             University of Kansas
Field Experiments – Antenna Setup




                                                                   4 ft


                                                      10 ft




        8 Antenna setup at SUMMIT camp in Greenland, July 2004
                                                                          18
                                            University of Kansas
    Results – Throughput




    Average throughput efficiency was observed to be 95%
    The above results are from the test cases where no call drops were experienced
    In event of call drops the effective throughput of the system will be less than the above values
                                                                                                   19
                                                                University of Kansas
Results – Throughput
FTP throughput observed during data transfer between the field camp and KU
          Size of file in MB       Approx. Upload Time      Effective Throughput in Kbps

                1.38                     0:11:24                       16.53

                3.77                     0:35:42                       14.42

                5.62                     0:46:12                       16.61

                15.52                    2:30:00                       14.12

                20.6                     3:00:00                       15.62

                35.7                     5:15:00                       15.47

                55.23                    9:00:00                       13.96



   Average throughput during the FTP upload of large files was observed to be 15.38 Kbps
   Due to call drops, the efficiency was reduced to ~80%
   Detailed TCP analysis based on IPERF and FTP data is in progress


                                                                                            20
                                                            University of Kansas
Results – Round Trip Time




                           Average RTT = 1.4 sec

                           Minimum observed RTT = 608 msec

                           Mean deviation = 800 msec



                                                          21
                                University of Kansas
    Results – Reliability: 14th July 12-hr test




                                                                                          Uptime %

                                                                                            89
                                                                                            95
                                                                                            96
                                                                                            97
                                                                                            97
                                                                                            97
                                                                                            97
                                                                                            98



    Call drop pattern during 8 Iridium – 8 Iridium DAV mode test for 12 hrs
    Percentage uptime with full capacity (8 channels) is 89% and with at least one modem is 98%
    Total number of primary call drops during 12 hrs = 4
    Average time interval between call drops is ~ 180 mins
                                                                                              22
                                                               University of Kansas
    Results – Reliability: 22nd July 32-hr test




                                                                                         Uptime %
                                                                                            85
                                                                                            92
                                                                                            93
                                                                                            93
                                                                                            94
                                                                                            94
                                                                                            94
                                                                                            96



    Call drop pattern during 8 Iridium – 8 Iridium DAV mode test for 32 hrs
    Percentage uptime with full capacity (8 channels) is 85% and with at least one modem is 96%
    Total number of primary call drops during 32 hrs = 24
    Average time interval between call drops is ~ 72 mins
                                                                                              23
                                                               University of Kansas
Results – Mobile tests

                                                         Iridium antennas




Iridium system mounted in an
autonomous vehicle (MARVIN)


                 Experiments monitored from another
                 vehicle through 802.11b link




                                                                             24
                                                      University of Kansas
    Results – Mobile tests




                                                                                         Uptime %

                                                                                            65
                                                                                            79
                                                                                            82
                                                                                            84
                                                                                            84
                                                                                            85
                                                                                            87
                                                                                            92




    Call drop pattern during 8 Iridium – 8 Iridium DAV mode test for 2 hrs
    Percentage uptime with full capacity (8 channels) is 65% and with at least one modem is 92%
    Average time interval between call drops is ~ 45 mins
    Average throughput = 18.6 Kbps, Average RTT = 1.8 sec
                                                                                                 25
                                                               University of Kansas
Applications
   Summer 2004 field experiments
   Communications data upload – up to 40 MB files
   Radar data uploads – up to 55 MB files
   Text chat with PRISM group at KU
   Video conference - real time audio/video
        Individual audio or video conference works with moderate quality with the
         commonly available codecs
   Outreach Use
        Daily Journal logs uploaded
        Daily Pictures uploaded
        Video clips uploaded
        Held video conference with science teachers/ virtual camp tour
   Wireless Internet access

                                                                                     26
                                                     University of Kansas
    Conclusions
    Integrated 8-channel system
         Works out of the box
         Reliable and fully autonomous operation

    The newly developed GUI based control software
         Reduced the field setup time, increased the ease of operation
         Suitable for operation by non-technical users

    System performance based on field experiments
         Average throughput with 8 channels is 18.6 Kbps, efficiency > 90%
         Average round trip time using DAV modes is 1.4 sec, significantly less than 2 sec of Iridium -PSTN
          configuration
         Average uptime with full capacity using DAV mode was 85 %; better than both non -DAV mode and
          PSTN mode
         Percentage system uptime (at least one mode) was ~95% for all the modes
         Average time interval between call drops is 60 mins and varies a lot.
    In conclusion, the throughput and delay performance of the system using Iridium-Iridium DAV
     mode is better than other data modes.

                                                                                                               27
                                                                        University of Kansas
Lessons Learned

   The call drop pattern
        Increased number of call drops in Iridium-Iridium mode
        The average time interval between call drops reduced from 100 minutes in case of 4
         Iridium-4 PSTN system to 60 minutes in case of 8 Iridium – 8 Iridium DAV system.
        Varies with time and weather
        Increased call drops in presence of strong radio interference

   Modem firmware failures
        random modem lock ups due to bug in firmware.
        Newer firmware upgrades reduced the number of such lock ups

   Primary modem failure
        No longer drops all the modems
        Just the one modem is lost
        System operates with remaining 7 modems

                                                                                              28
                                                            University of Kansas
    Continuing Work
    Signal Strength issues
         Reduce the number of call drops

         Reduce signal attenuation at the server

    Server Software
         GUI based server management software

         Increase reliability during field operations

         Ease of operation and use by non-technical personnel

    Delay Tolerant Networks
         Communication networks tolerant to inherent delays

         Set of protocol and architectures well suited to intermittent links

         Supports communication in heterogeneous sensor webs such as polar sensor web

         Adapt the evolving DTN technologies to address polar communication issues?

                                                                                         29
                                                                 University of Kansas

				
DOCUMENT INFO