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University of Kansas
Alternative Communication Networking in Polar Regions
Abdul Jabbar MohammadNandish Chalishazar
Victor Frost Glenn Prescott
International Symposium on Advanced Radio Technologies, Colorado 2004
Information and Telecommunication Technology CenterDepartment of Electrical Engineering and Computer Science
University of KansasLawrence, 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 University of
Kansas
University of Kansas 2
Presentation Outline
Motivation
Introduction
Multi-Channel Iridium System
Long range WI-FI System (work done by Nandish Chalishazar)
Field Experiments and Results
Conclusions
University of Kansas 3
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 University of Kansas
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
University of Kansas 4
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
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 (1-20) result in extremely large field
equipment.
May not be readily available20 m diameter Marisat/GOES antenna at South Pole
Source: http://cfa-www.harvard.edu/~aas/SPUC/02/presentations/SATCOM.ppt
[Source:http://adelie.harvard.edu/spole/]
University of Kansas 5
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 8.20
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
University of Kansas 6
Multi-channel Iridium System - Design
Iridium Gateway
PSTN
US
B-S
ER
IAL
I. Modem 3
I. Modem 4
I. Modem 2
I. Modem 1 Antenna G
ridM
ulti-port P
CI card
Remote System
PPP client
Local System
PPP Server
Modem Pool
Remote Subsystem
Local Subsystem
University of Kansas 7
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 System Local System
point-to-point satellite links
University of Kansas 8
Multi-channel Iridium System – Network Architecture
NGRIP Camp, Greenland
Local Network, University of Kansas
World Wide Web
User 2
User 3
User 1
ppp0 eth0
PPP Server
ppp0 eth0
PPP Client
P-T-P Satellite link
Default Router
(Default gateway)(Default gateway)Guser 4
Guser 3
Guser 2G`user 1
Camp WI-FI
100 Mbps Ethernet
100 Mbps Ethernet
University of Kansas 9
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 3600 and vertical beam width of 70.
1-Watt bidirectional amplifier with AGC and Tx of 29.3 dBm
University of Kansas 10
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
University of Kansas 11
Field Experiments – Iridium System
4-channel system setup Antenna Setup
Field experiments conducted at NGRIP, Greenland (75 06’ N, 42 20’ W) in Summer 2003
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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
% Loss
RTT (sec)
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
University of Kansas 13
Iridium Results – Throughput
Throughput Vs Number of Modems
2.1
4.25
6.88
9.26
0123456789
10
1 2 3 4Number of modems
Thro
ughp
ut
Tools used – TTCP, IPERF
Throughput varies to some
extend due to RTT variation
Efficiency > 90%
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
Effective throughputs during large file transfers
(Kbp
s)
University of Kansas 14
Iridium Results – Reliability: 24 hr test
Call drop events vs. Time
21:1
5
21:5
7
22:3
9
23:2
1
0:0
3
0:4
5
1:2
7
2:0
9
2:5
1
3:3
3
4:1
5
4:5
7
5:3
9
6:2
1
7:0
3
7:4
5
8:2
7
9:0
9
9:5
1
10:3
3
11:1
5
11:5
7
12:3
9
13:2
1
14:0
3
14:4
5
15:2
7
16:0
9
16:5
1
17:3
3
18:1
5
18:5
7
19:3
9
20:2
1
21:0
3
Time
Ca
ll d
rop
eve
nt
Modem up times during 24 hour test
0
1
2
3
4
21:1
5
22:0
0
22:4
5
23:3
0
0:1
5
1:0
0
1:4
5
2:3
0
3:1
5
4:0
0
4:4
5
5:3
0
6:1
5
7:0
0
7:4
5
8:3
0
9:1
5
10:0
0
10:4
5
11:3
0
12:1
5
13:0
0
13:4
5
14:3
0
15:1
5
16:0
0
16:4
5
17:3
0
18:1
5
19:0
0
19:4
5
20:3
0
21:1
5
Time
Nu
mb
er
of
on
lin
e
mo
de
ms
Time intervalbetween call drops
(minutes)146 106 114 50 25 84 89 8 7 7 17 11 137 618
Total :
13 Call
drops
80.6
91.8
94.7
96.8
Uptime %
Call drops on the first modem
University of Kansas 15
Field Experiments – WI-FI System
Base Station Mobile Vehicle
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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
University of Kansas 17
WI-FI system Results – Extended LAN
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
Variation of RSS with distance Base antenna height=3m and mobile antenna height=1.4m GPS error =10m
Variation of RSS with distanceBase antenna height=3m and mobile antenna height=1.4m GPS error =10m
University of Kansas 18
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.
University of Kansas 19
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
University of Kansas 20
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,
pole-to-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.
