Alternative Communication Networking in Polar Regions Abdul Jabbar Mohammad Nandish Chalishazar Victor Frost Glenn Prescott International Symposium on Advanced Radio Technologies, Colorado 2004 Information and Telecommunication Technology Center Department of Electrical Engineering and Computer Science Lawrence, KS Sponsors:National Science Foundation (grant #OPP-0122520), the National Aeronautics and Space Administration (grants #NAG5-12659 and NAG5-12980), the Kansas Technology Enterprise Corporation, and the
Presentation Outline Motivation Introduction Multi-Channel Iridium System Long range WI-FI System (work done by Nandish Chalishazar) Field Experiments and Results Conclusions 2
Motivation Polar Radar for Ice Sheet Measurements (PRISM) : developing intelligent remote sensing technology to determine thickness of ice sheets and ice-bedrock interface in Greenland and Antarctica. The system comprises of a sensor web deployed over intelligent rovers. Inter-rover communication Reliable, high bandwidth communications required between nodes separated by 8 Km on the ice Data communication between the field camp and Data telemetry and access to University and web resources from field Public outreach Generic data communication for Remote field research Mainstream communication system for polar science expeditions, field camps in Arctic/Antarctic and other research purposes Government and security use 3
Introduction Satellite Communication Polar regions do not have conventional communication facilities and are not serviced by most of the major broadband satellite systems (like Inmarsat, Intelsat, Globalstar). NASA satellites like ATS3, LES9, GOES, TDRS 1,and MARISAT2 provide broadband [Source:http://adelie.harvard.edu/spole/] access to Polar Regions Geo-synchronous, they have a limited visibility window at Poles typically 10-13 hrs/day. High satellite altitude and low elevation angles (1-2 0 ) result in extremely large field equipment. May not be readily available 20 m diameter Marisat/GOES antenna at South Pole Source: http://cfa-www.harvard.edu/~aas/spuc/02/presentations/satcom.ppt 4
Introduction - Iridium Satellite System Iridium The only commercial satellite system with true pole-to-pole coverage 66 low earth orbiting (LEO) satellites Onboard satellite switching technology Minimum elevation angle of 8.2 0 Average satellite view time ~ 9-10 minutes Access scheme is a combination of FDMA and TDMA Problem: Since it provides a low bandwidth of 2.4 Kbps, it is not practical to be used as a main stream/ life-line communication system Solution: Inverse Multiplexing - Combine multiple satellite links using multi-link point to point protocol (MLPPP) to obtain a single logical channel of aggregate bandwidth 5
Multi-channel Iridium System - Design Remote System PPP client USB-SERIAL I. Modem 1 I. Modem 2 I. Modem 3 I. Modem 4 Antenna Grid Iridium Gateway Remote Subsystem Local System PPP Server Multi-port PCI card Modem Pool PSTN Local Subsystem 6
Multi-channel Iridium System Protocol Stack Remote System Local System Application Application HTTP, FTP, SSH HTTP, FTP, SSH TCP TCP IP IP PPP/MLPPP Physical Modems point-to-point satellite links PPP/MLPPP Physical Modems 7
Multi-channel Iridium System Network Architecture World Wide Web NGRIP Camp, Greenland 100 Mbps Ethernet Default Router (Default gateway) PPP Server (Default gateway) PPP Client Guser 4 eth0 ppp0 P-T-P Satellite link ppp0 eth0 User 2 100 Mbps Ethernet User 1 Guser 3 User 3 Camp WI-FI Guser 2 G`user 1 Local Network, 8
WI-FI system Range of the commercial off-the-shelf systems is few hundred meters not enough Increase the range of the 802.11b link up to 8 Km - amplification of the signal is required to overcome the propagation losses The two ray propagation model predicts forth power loss with distance over ice Also the received signal strength increases by 6 db on doubling the height of the antenna Combination of high gain antenna and RF amplifier can help to achieve the required signal strength 9-dBi vertical collinear antenna horizontal beam width of 360 0 and vertical beam width of 7 0. 1-Watt bidirectional amplifier with AGC and Tx of 29.3 dbm 9
WI-FI System Basic LAN Central Access point with high gain antenna and bidirectional amplifier End users use off-the-shelf 802.11b wireless cards to access the Iridium based Internet Range ~ 1 Km Extended LAN Both ends of the communication antennas need amplifiers and high gain antennas connected to the wireless cards Range ~ 8 Km Bandwidth decreases with distance 10
Field Experiments Iridium System Field experiments conducted at NGRIP, Greenland (75 06 N, 42 20 W) in Summer 2003 4-channel system setup Antenna Setup 11
Iridium Results Delay and Loss Measurement Ping tests between the two machines at the end of the of satellite link Transmission + Propagation delay = 524msec Test results show an average RTT delay of 1.8 sec, Random delay variation and high mean deviation Causes may include - inter-satellite switching, processing at the gateway, distance between the user and satellite and distance between the satellites (ISL) Packets sent Packets received RTT (sec) % Loss Avg Min Max Mdev 50 50 0 1.835 1.347 4.127 0.798 100 100 0 1.785 1.448 4.056 0.573 100 100 0 2.067 1.313 6.255 1.272 200 200 0 1.815 1.333 6.228 0.809 12
Iridium Results Throughput Tools used TTCP, IPERF Throughput varies to some extend due to RTT variation Efficiency > 90% Effective throughputs during large file transfers File Size (MB) Upload Time (min) Throughput (bits/sec) 0.75 11 9091 1.5 28 7143 1.6 23 9275 2.3 45 6815 2.5 35 9524 3.2 60 7111 (Kbps) Throughput 10 9 8 7 6 5 4 3 2 1 0 2.1 Throughput Vs Number of Modems 4.25 6.88 1 2 3 4 Number of modems 9.26 13
Iridium Results Reliability: 24 hr test Call Call drops drop on the events first modem vs. Time Total : 13 Call drops 21:15 21:57 22:39 23:21 0:03 0:45 1:27 2:09 2:51 3:33 4:15 4:57 5:39 6:21 7:03 7:45 8:27 9:09 9:51 10:33 11:15 11:57 12:39 13:21 14:03 14:45 15:27 16:09 16:51 17:33 18:15 18:57 19:39 20:21 21:03 Call drop event Time 4 3 2 1 0 Modem up times during 24 hour test Uptime % 80.6 91.8 94.7 96.8 21:15 22:00 22:45 23:30 0:15 1:00 1:45 2:30 3:15 4:00 4:45 5:30 6:15 7:00 7:45 8:30 9:15 10:00 10:45 11:30 12:15 13:00 13:45 14:30 15:15 16:00 16:45 17:30 18:15 19:00 19:45 20:30 21:15 Time Time interval between call drops (minutes) 146 106 114 50 25 84 89 8 7 7 17 11 137 618 14 Number of online modems
Field Experiments WI-FI System Base Station Mobile Vehicle 15
WI-FI system Results Basic WLAN Variation of SNR and throughput in basic (infrastructure) WLAN Infrastructure LAN Wireless clients with in the camp access the Iridium system Variation of SNR with distance Internet throughput does not vary with SNR 16
WI-FI system Results Extended LAN Variation of RSS with distance Base antenna height=3m and mobile antenna height=1.4m GPS error =10m Variation of RSS with distance Base antenna height=3m and mobile antenna height=1.4m GPS error =10m Measurements are carried out using a fixed base station and a mobile client (peer-to-peer) Received signal strength variation matches very well with the theoretical two-ray propagation model The effects of using a multi-element antenna is accounted for in the theoretical prediction 17
WI-FI system Results Extended LAN Variation of signal to noise ratio along track 1 for equal antenna heights of 1.4, 2, 3 and 5 at the base station and mobile vehicle Corresponding TCP throughput measured every 0.5 Km Throughput varies from 4.9 0.2 Mbps depending on the SNR Throughput does not decrease monotonically with packet errors inherent in a 802.11b link. 18
Applications - Wireless Internet Data telemetry Wireless Internet/email access Download critical software on field ( up to 7.2 MB) Obtain expert help while on the field Collaborate field experiments with mainland research facilities Public outreach video clips, daily reports, etc. General camp purpose: sending drawings to order spares for a broken caterpillar, excel spreadsheet for food order, general press releases downloading weather reports for planning C-130 landings 19
Conclusions Multi-channel Iridium communication could be used to reliable provide data and Internet access to Polar Regions. This system is easily scalable, lightweight, readily available and has round the clock, poleto-pole coverage. The developed link management software ensures fully autonomous and reliable operation The Iridium system can be integrated with reliable long range 802.11b wireless to provide connectivity for distances up to 8 Km The validity of two-ray propagation model over flat ice sheets in Polar Regions is proved The system provided for the first time, wireless data and Internet access to NGRIP camp in Greenland. 20
Questions? Comments? THANK YOU jabbar@ittc.ku.edu 21