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
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	Iridium Based Data Communication
6	Multi-channel Iridium System � Protocol Stack
7	4-Channel Iridium System - Design
8	4-Channel Iridium System� Testing at NGRIP, Greenland-2003
9	4-Channel Iridium System -2003 Conclusions
10	4-Channel Iridium System -2003 Conclusions
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
13	8-channel Iridium System � Client Software
14	8-channel Iridium System � Client GUI
15	8-channel Iridium System � Client GUI
16	8-channel Iridium System �Network Architecture
17	Field Experiments� � System Implementation
18	Field Experiments � Antenna Setup
19	Results � Throughput
20	Results � Throughput
21	Results � Round Trip Time
22	Results � Reliability: 14th July 12-hr test
23	Results � Reliability: 22nd July 32-hr test
24	Results � Mobile tests
25	Results � Mobile tests
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?