# Presentation: 090496

## 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**
**University of Kansas**
**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 University of Kansas**** **

## Presentation Outline

- Motivation
- Introduction
- Multi-Channel Iridium System
- Long range WI-FI System   *(work done by Nandish Chalishazar)*
- Field Experiments and Results
- Conclusions

## 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

## 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 available

- 20 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/]***

## 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

## Multi-channel Iridium System - Design

- Iridium Gateway

- Multi-port PCI card

- Remote System
- PPP client

-  Local System
- PPP Server

- Modem Pool

**Remote Subsystem**

**Local Subsystem**

## 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

## Multi-channel Iridium System – Network Architecture

**NGRIP Camp, Greenland**

**Local Network, University of Kansas**

**User 2**

** ****User 3**

**User 1**

- ppp0

- eth0

**           ****PPP Client**

**P-T-P Satellite link**

**Default Router**

- (Default gateway)

- (Default gateway)

**Guser 4**

- Camp   WI-FI

- 100 Mbps Ethernet

- 100 Mbps Ethernet

## 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

## 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

## 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

## 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 |

## Iridium Results – Throughput

- 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

- (Kbps)

## Iridium Results – Reliability: 24 hr test

| Time interval
between 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**

## Field Experiments – WI-FI System

- Base Station

- Mobile Vehicle

## 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

## 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 distance**
**Base antenna height=3m and mobile antenna height=1.4m GPS error =10m**

## 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.

## 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

## 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.

## Questions ? Comments?

- THANK YOU
- jabbar@ittc.ku.edu