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Multi-Link Iridium Satellite Data Communication System for Polar Research

Multi-Link Iridium Satellite Data Communication System for Polar Research. Abdul Jabbar Mohammad (September 15, 2005). Motivation - PRISM. Polar Radar for Ice Sheet Measurements (PRISM) Field experiments in Greenland and Antarctica Data telemetry from the field to the University

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Multi-Link Iridium Satellite Data Communication System for Polar Research

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  1. Multi-Link Iridium Satellite Data Communication System for Polar Research Abdul Jabbar Mohammad (September 15, 2005)

  2. 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

  3. Satellite Data Communication • Commercial Satellite systems • No coverage or intermittent coverage • Prohibitively expensive ($3 - $30 per MB) • Special Purpose Satellite systems • ATS3, LES9, GOES, TDRS 1,and MARISAT2 • Broadband Access • Geo-synchronous : Limited visibility (10-13 hrs/day) • Low elevation angles : extremely large ground terminals Inmarsat Globalstar

  4. 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

  5. Mux App 1 High Bandwidth Link App 2 App 3 Multiplexing Low Bandwidth Links Inv-Mux App 1 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) Inverse multiplexing

  6. Multi-channel Iridium System – Protocol Stack Remote System Local System point-to-point satellite links

  7. Remote System PPP client Iridium Gateway USB-SERIAL I. Modem 1 Antenna Grid I. Modem 2 I. Modem 3 I. Modem 4 Remote Subsystem Local System PPP Server Multi-port PCI card PSTN Modem Pool Local Subsystem 4-Channel Iridium System - Design • 4 Iridium – 4 PSTN data configuration • Discrete components • Patch antennas • Control software on a rugged Laptop

  8. 4-Channel Iridium System Testing at NGRIP, Greenland-2003 4-Channel Iridium System at NGRIP Antenna setup at NGRIP

  9. 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

  10. 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

  11. 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

  12. 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 • Power input : 120 V AC • Replication Costs : ~$18,000 9”

  13. 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

  14. 8-channel Iridium System – Client GUI

  15. 8-channel Iridium System – Client GUI

  16. 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 100 Mbps Ethernet User 2 User 1 user 3 user 1 User 3 Camp WI-FI user 2 World Wide Web ITTC Network, University of Kansas 8-channel Iridium System –Network Architecture

  17. Field Experiments – System Implementation 8-Channel system in a weather-port at SUMMIT camp in Greenland, July 2004

  18. Field Experiments – Antenna Setup 4 ft 10 ft 8 Antenna setup at SUMMIT camp in Greenland, July 2004

  19. 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

  20. Results – Throughput FTP throughput observed during data transfer between the field camp and KU • 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

  21. Results – Round Trip Time • Average RTT = 1.4 sec • Minimum observed RTT = 608 msec • Mean deviation = 800 msec

  22. Uptime % 89 95 96 97 97 97 97 98 Results – Reliability: 14th July 12-hr test • 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

  23. 85 92 93 93 94 94 94 96 Results – Reliability: 22nd July 32-hr test Uptime % • 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

  24. Results – Mobile tests Iridium antennas Iridium system mounted in an autonomous vehicle (MARVIN) Experiments monitored from another vehicle through 802.11b link

  25. Uptime % 65 79 82 84 84 85 87 92 Results – Mobile tests • 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

  26. 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

  27. 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.

  28. 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

  29. 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?

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