DBCP Workshop, Chennai October 2004 David Meldrum and Duncan Mercer Scottish Association for Marine...
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![Page 1: DBCP Workshop, Chennai October 2004 David Meldrum and Duncan Mercer Scottish Association for Marine Science Further refinements in the use.](https://reader036.fdocuments.us/reader036/viewer/2022070307/551a94cb55034643688b5edc/html5/thumbnails/1.jpg)
DBCP Workshop, Chennai October 2004
David Meldrum and Duncan Mercer
Scottish Association for Marine Sciencewww.sams.ac.uk
Further refinements in the use of Iridium for polar applications
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DBCP Workshop, Chennai October 2004
Satcom systems available to buoy operatorsInmarsat D+ Pager GEO < 1 kbyte/day
GOES, Meteosat
Messaging
GEO < 5 kbyte/day
Argos Messaging
LEO < 5 kbyte/day
AprizeSat Messaging
LEO ??
Inmarsat C Messaging
GEO < 10 kbyte/day
Orbcomm Messaging
LEO < 50 kbyte/day
Iridium Voice Big LEO
1 Mbyte/hr
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DBCP Workshop, Chennai October 2004
Features of Iridium• 66+ satellites in low earth orbit• Designed for voice communications• Real-time: inter-satellite comms• 2-way• True global• Compact antenna• Future more or less assured• Detested by Argos
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DBCP Workshop, Chennai October 2004
Iridium constellation
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DBCP Workshop, Chennai October 2004
Visibility comparison : Argos and Iridium
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0 10 20 30 40 50 60 70 80 90
Latitude
Min
s/d
ay
Argos 2-sat vis
Iridium 66-sat vis
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DBCP Workshop, Chennai October 2004
Iridium in the GreenIce project• Climate change – is the Arctic ice thinning?
• Average ice thickness difficult to measure
• Nagurny theory: spectrum of swell waves penetrating ice is a function of area averaged thickness
• Small waves (λ = 1500m , 4mm pk-to-pk)
• Need to resolve 1 radian tilt (strain 4x10-8)
• 75kbyte/day of spectral and other data
• Latest deployments spring/summer 2004
• Met data on GTS via Metocean SVP-Bs and Argos
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DBCP Workshop, Chennai October 2004
Iridium – modes of access• Dial-up over voice circuit
• Modem to modem• ~300bytes/s• ~$1/min connect time • A bit flaky – unexplained call drops
• Short Burst Data (SBD)• E-mail service• Mobile originated packet transfer• ~2 kbyte max packet size• ~$1/kbyte• More or less bomb-proof
• Short Message Service• Can be used to wake mobile up for SBD xfer
• Direct Internet• Various flavours….
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DBCP Workshop, Chennai October 2004
Short Burst Data Pathways
• Simple AT commands
IRIDIUM NETWORK
IRIDIUM NETWORK
INTERNET
INTERNET
SENSOR
USER
MODEMTX Buffer
RX Buffer
+SBDWB
+SBDRB+SBDI
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DBCP Workshop, Chennai October 2004
Example e-mail received by user (MO message)
From: <Iridium SBD Service (Tempe, AZ)>
Sent: Tue, 23 Sep 2003 22:02:24
Subject: SBD Msg From Unit: 300090807080903
MOMSN:152
MTMSN:0
Session Status: TRANSFER OK
Message Size (bytes): 1960
Unit Location: Lat = 56.457321 Long = -5.458788
CEPradius = 2
Message is attached.
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DBCP Workshop, Chennai October 2004
Email delivery time
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14 16 18 20 22 24 26 28 30 32 34secondsseconds
SBD Delivery Latency
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DBCP Workshop, Chennai October 2004
Iridium - energy consumption rate vs file size
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File size (kbyte)
Co
nsu
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yte
)
Dial-up
SBD
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DBCP Workshop, Chennai October 2004
Iridium - $ consumption rate vs file size
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Co
nsu
mp
tio
n r
ate
($/
kb
yte
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Dial-up
SBD
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DBCP Workshop, Chennai October 2004
SBD vs Dial Up
•SBD easy to SBD easy to
implement….implement….
•Cost penalty?Cost penalty?
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DBCP Workshop, Chennai October 2004
SBD vs Dial Up
•SBD easy to SBD easy to
implement….implement….
•Cost penalty?Cost penalty?
•$115k for 6 months!$115k for 6 months!
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DBCP Workshop, Chennai October 2004
Revisit dial-up!
• Charged at 1$/min, 10¢/kbyte or better
• Identify cause of call drops• Modify ZMODEM protocol• Create outbound file queue to deal
with remaining call drops• Establish dedicated modem and
server• Array of 5 platforms has run without
problem since May
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
Impulse event – tilt record
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
History repeats itself…• Early problems for the Argos user
• Why buy Argos?• Argos promises to meet user need
• The system works!• How does it work?• Will it do a new task?• Suck it and see
• The system doesn’t work…• God Only Knows (GOK)• Satellite Operator Only Knows (SOOK)• Whom do you contact?
• The system costs more than you can afford…
• Tariff and invoices incomprehensible
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DBCP Workshop, Chennai October 2004
One solution – maybe for Iridium too?
• DBCP Technical Co-ordinator (1987)• Based at Argos Toulouse• Access to all elements of chain, incl GTS• Access to Argos technical team
• JTA negotiations• Discounted price for global bulk purchase• Tariff and invoices still incomprehensible• System still costs more than you can
afford
• At least the mess is partly of our own making….
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DBCP Workshop, Chennai October 2004
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DBCP Workshop, Chennai October 2004
IRIDIUM