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University of Kansas Multi-Link Iridium Satellite Data Communication System for Polar Research Abdul Jabbar Mohammad (September 15, 2005) Slide 2 University of Kansas 2 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 Motivation - PRISM Slide 3 University of Kansas 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 Slide 4 University of Kansas 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 Slide 5 University of Kansas 5 Iridium Based Data Communication App 3 App 2 App 1 Mux High Bandwidth Link Multiplexing App 1 Inv-Mux Low Bandwidth Links 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 Slide 6 University of Kansas 6 Multi-channel Iridium System Protocol Stack Application HTTP, FTP, SSH TCP IP PPP/MLPPP Physical Modems Application HTTP, FTP, SSH TCP IP PPP/MLPPP Physical Modems Remote SystemLocal System point-to-point satellite links Slide 7 University of Kansas 7 4-Channel Iridium System - Design Iridium Gateway PSTN USB-SERIAL I. Modem 3 I. Modem 4 I. Modem 2 I. Modem 1 Antenna Grid Multi-port PCI card Remote System PPP client Local System PPP Server Modem Pool Remote Subsystem Local Subsystem 4 Iridium 4 PSTN data configuration Discrete components Patch antennas Control software on a rugged Laptop Slide 8 University of Kansas 8 4-Channel Iridium System Testing at NGRIP, Greenland-2003 4-Channel Iridium System at NGRIPAntenna setup at NGRIP Slide 9 University of Kansas 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 Slide 10 University of Kansas 10 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 4-Channel Iridium System -2003 Conclusions Slide 11 University of Kansas 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 Slide 12 University of Kansas 12 8-channel Iridium System Integrated Unit 9 19 24 Bottom View Top View Front View Dimension: 9x19x24 inch Weight : 50 lbs Operating temp: -30 to 60 c Power input : 120 V AC Replication Costs: ~$18,000 Slide 13 University of Kansas 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 Slide 14 University of Kansas 14 8-channel Iridium System Client GUI Slide 15 University of Kansas 15 8-channel Iridium System Client GUI Slide 16 University of Kansas 16 8-channel Iridium System Network Architecture Polar Camp, Greenland/Antarctica ITTC Network, University of Kansas World Wide Web User 2 User 3 User 1 ppp0eth0 PPP Server ppp0 eth0 PPP Client P-T-P Satellite link ITTC Default Router (Default gateway) user 4 user 3 user 2 user 1 Camp WI-FI 100 Mbps Ethernet Slide 17 University of Kansas 17 Field Experiments System Implementation 8-Channel system in a weather-port at SUMMIT camp in Greenland, July 2004 Slide 18 University of Kansas 18 Field Experiments Antenna Setup 4 ft 10 ft 8 Antenna setup at SUMMIT camp in Greenland, July 2004 Slide 19 University of Kansas 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 Slide 20 University of Kansas 20 Results Throughput Size of file in MBApprox. Upload TimeEffective Throughput in Kbps 1.380:11:2416.53 3.770:35:4214.42 5.620:46:1216.61 15.522:30:0014.12 20.63:00:0015.62 35.75:15:0015.47 55.239:00:0013.96 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 Slide 21 University of Kansas 21 Results Round Trip Time Average RTT = 1.4 sec Minimum observed RTT = 608 msec Mean deviation = 800 msec Slide 22 University of Kansas 22 Results Reliability: 14th July 12-hr test Uptime % 89 95 96 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 Slide 23 University of Kansas 23 Results Reliability: 22nd July 32-hr test Uptime % 85 92 93 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 Slide 24 University of Kansas 24 Results Mobile tests Iridium system mounted in an autonomous vehicle (MARVIN) Experiments monitored from another vehicle through 802.11b link Iridium antennas Slide 25 University of Kansas 25 Results Mobile tests Uptime % 65 79 82 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 Slide 26 University of Kansas 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 Slide 27 University of Kansas 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. Slide 28 University of Kansas 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 Slide 29 University of Kansas 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?