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MultiLink Iridium Satellite Data Communication System

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Title: MultiLink Iridium Satellite Data Communication System


1
Multi-Link Iridium Satellite Data Communication
System
  • Overview, Performance and Reliability from Summer
    2004 SUMMIT, Greenland Field Experiments
  • July 14-July 25, 2004
  • Abdul Jabbar Mohammad, Said Zaghloul, Graduate
    Research Assistants
  • Dr.Victor Frost, Dan F. Servey Distinguished
    Professor
  • (August 22, 2003)

2
Presentation Outline
  • Previous Work
  • 4-Channel System
  • Conclusions from 2003 Field Experiments
  • 8-Channel Iridium System
  • Design
  • Integrated Unit
  • GUI Software
  • Analysis
  • Network Architecture
  • 2004 Field Experiments
  • Field Implementation
  • Results
  • Conclusions and Future Work

3
4-Channel Iridium System (Tested in Summer 2003)
  • 4 Iridium 4 PSTN data configuration
  • Discrete components
  • Patch antennas
  • Control software on a rugged Laptop

4
Conclusions from 2003 field experiments
  • Developed a reliable multi-channel data
    communication system based on Iridium satellites
    that provide round the clock, pole-to-pole
    coverage.
  • Developed console based link management software
    that ensures fully autonomous and reliable
    operation
  • An end-to-end network architecture providing
    Internet access to science expeditions in Polar
    Regions was demonstrated.
  • The system efficiency was observed to be gt90.
    With 4-modems the average end-to-end throughput
    was found to be 9.26 Kbps
  • The round trip time of the system in Iridium-PSTN
    configuration was significant 1.8 sec
  • The average up-time of the overall connection was
    approx 90. The average time interval between
    primary call drops was 100 minutes
  • Mobile tests showed performance very similar to
    that of stationary system up to speeds of 20mph
  • 4-Iridium to 4-PSTN configuration was found to be
    stable of autonomous operation

5
Conclusions from 2003 field experiments
  • The USB-to-serial converter used for multiple
    serial ports was not stable resulting in system
    failures.
  • Interaction of PPP level compression with control
    software results in corrupted modem termination,
    resulting in significant packet loss
  • Identified areas for additional research
  • Evaluate the new data-after-voice (DAV) service
    from Iridium
  • Improve the user friendliness of the system
  • Research into the spacing and sharing of antennas
    to reduce the antenna footprint
  • Increase the the system capacity by scaling the
    system from 4 to 8 channels
  • Develop a fully integrated plug and play system
    that can be deployed easily in the field

6
8-channel Iridium System Design Elements
  • Integrated 8 Iridium modems and all the
    components in an 19 rack mount unit.
  • On-board computer to run the control software
  • Single board EBX format system ( P-III, 1 GHz,
    512 MB RAM)
  • Extended temperature operation (-300 C to 800 C
    )
  • PC104 type multi-port serial card with 8 DB9
    ports (extended temp operation)
  • Integrated 5x4 LCD screen, front panel flips
    down to hold the keyboard/mouse
  • Single linear power supply for the 8 modems and
    on-board computer
  • Developed a new GUI based management/control
    software, that configures the unit in all the
    data modes a) Iridium-Iridium DAV mode, b)
    Iridium-Iridium data mode, c) Iridium-PSTN mode
  • Replaced the patch antennas with inverted cone
    antennas that can be easily mounted on field and
    do not need a external ground plane.

7
8-channel Iridium System Integrated Unit
Bottom View
Top View
19
24
Front View
  • Dimension 9x19x24 inch
  • Weight 50 lbs
  • Operating temp -30 to 60 c
  • Power input 120 V AC
  • Replication Costs 18,000

9
8
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

9
8-channel Iridium System Client GUI
10
8-channel Iridium System Client GUI
11
8-channel Iridium System Analysis
Machine A
Machine B
  • System Model
  • Application FTP, HTTP
  • Agent TCP, UDP
  • MLPPP
  • 8 Modem Links

App
App
Agent
Agent
Iridium Network
  • Modems Model
  • Each link has a dropping probability
  • Each link has a probability of error

8 Modem Links
MLPPP
MLPPP
12
8-channel Iridium System Network Architecture
13
Field Experiments System Implementation
8-Channel system in a weather-port at SUMMIT camp
in Greenland, July 2004
14
Field Experiments Antenna Setup
4 ft
10 ft
8 Antenna setup at SUMMIT camp in Greenland, July
2004
15
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

16
Results Throughput
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

17
Results Round Trip Time
  • Average RTT 1.4 sec
  • Minimum observed RTT 608 msec
  • Mean deviation 800 msec
  • Detailed analysis in progress

18
Results Reliability 14th July 12-hr test
  • 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

19
Results Reliability 22nd July 32-hr test
Uptime
  • 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

20
Results Reliability 19th July 6-hr test
  • Call drop pattern during 8 Iridium 8 PSTN data
    mode test for 32 hrs
  • Percentage uptime with full capacity (8 channels)
    is 67 and with at least one modem is 90
  • Total number of primary call drops during 6 hrs
    9
  • Average time interval between call drops is 35
    mins

21
Results Mobile tests
Iridium antennas
Iridium system mounted in an autonomous vehicle
(MARVIN)
Experiments monitored from another vehicle
through 802.11b link
22
Results Mobile tests
  • 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 2
    sec

23
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

24
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 gt 90
  • Average round trip time using DAV modes is 1.4
    sec, significantly less than 1.8 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.

25
Lessons Learned
  • 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.
  • The call drop pattern as seen in number of
    online modems vs. time characteristics varies
    over time. (detailed study in progress)
  • Modem firmware failures were experience for the
    first time. Modem locks up randomly and needs
    power cycling. This problem is not very severe
    and occurred less than 5 times during the field
    experiments . Further, this issues has been
    noticed by the other researchers using Iridium
    for field work.
  • Mounting of antennas on the mobile vehicle could
    be improved to increase stability for long
    duration experiments. While the current mounting
    works for short duration tests, it is not stable
    for permanent field operation
  • Due to a bug in linux pppd software, a call drop
    on the primary modem still causes the entire
    bundle to drop.

26
Future Work to Understand and Enhance the MLPPP
Iridium System
  • The performance of network using the
    Iridium/MLPPP needs to be evaluated
  • A system model is needed in order to explain the
    network behavior and to develop enhancements to
    the system
  • Call drops needs to be categorized and reasons
    for call drops need to be studied
  • Due to poor signal strength (Low SNR)
  • Due to Handovers (inter-satellite and
    intra-cell)
  • Other reasons
  • The performance of the TCP RTT measurement
    algorithm needs to be evaluated over the MLPPP
    Iridium link

27
Future Work to Understand and Enhance the MLPPP
Iridium System
  • Analyze call drop pattern. Experiments at ITTC to
    validate the number of call drops.
  • Upgrade modem firmware (as it becomes available)
    to solve the problem of failures. Else the
    control software should be modified so that it
    can recognize modem failures and cycle power to
    that modem.
  • Develop user-friendly GUI based server software
    (similar to the client software) to increase the
    functionality and ease of operation
  • Research the pppd bug that causes the entire
    bundle to drop on the event of a primary modem
    call drop. Modification of PPP networking code
    could be one solution.
  • While detailed TCP analysis is in progress, it is
    evident that a call drop results in a degradation
    in the system performance. This effect could
    increase as the propagation distance/delay (e.g.
    data transfer between Kansas and Antarctica),
    understanding and then being able to predict such
    degradations is needed.

28
Future Work-Research
  • Delay Tolerant Networking (DTN) Research of new
    network protocols and methods for reliable data
    communication among extreme and
    performance-challenged environments. The
    efficiency of the standard internet protocols
    decreases considerably with propagation distance
    and intermittent connectivity, making them
    unsuitable for very long distance/intermittent
    communication.
  • Communications from Polar Regions involves
    similar problems as addressed by DTN, e.g.,
    connectivity over low speed links and
    intermittent connectivity over high speed links.
  • Methods developed for networks with intermittent
    connectivity would be suitable for communication
    over satellite links with frequent call drops as
    experienced with Iridium.

29
Future Work-Research
  • Typical DTN applications involve low bandwidth
    intermittent (satellite) link and high bandwidth
    conventional (Internet) links as parts of the
    same network. Hence, interoperability is a major
    issue.
  • A new suite of communication protocols is being
    researched by the Consultative Committee for
    Space Data Systems (CCSDS) and Delay Tolerant
    Networking Research Group (DTNRG). The CCSDS File
    Delivery Protocol concentrates on a tiered
    architecture building over the existing regional
    protocols wherever possible. Adapting the
    protocols being developed by CCSDS and DTNRG for
    polar research in needed.

30
Future Work-Research Issues
  • Can the evolving DTN technologies be adapted to
    enhance communications in polar regions, if so
    how?
  • How can optimum DTN system parameters be
    determined?
  • What is reliability vs. efficiency of the
    developed protocols?
  • Can the Iridium be used to evaluate the new DTN
    protocols?
  • Are existing protocols (like CFDP) over satellite
    networks (Iridium) suitable for polar
    communications?
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