dbcp workshop, chennai october 2004 david meldrum and duncan mercer scottish association for marine...
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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
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
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
DBCP Workshop, Chennai October 2004
Iridium constellation
DBCP Workshop, Chennai October 2004
Visibility comparison : Argos and Iridium
0
200
400
600
800
1000
1200
1400
0 10 20 30 40 50 60 70 80 90
Latitude
Min
s/d
ay
Argos 2-sat vis
Iridium 66-sat vis
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
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….
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
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.
DBCP Workshop, Chennai October 2004
Email delivery time
0
100
200
300
400
500
600
14 16 18 20 22 24 26 28 30 32 34secondsseconds
SBD Delivery Latency
DBCP Workshop, Chennai October 2004
Iridium - energy consumption rate vs file size
0
20
40
60
80
100
0.01 0.1 1 10 100 1000
File size (kbyte)
Co
nsu
mp
tio
n r
ate
(J/
kb
yte
)
Dial-up
SBD
DBCP Workshop, Chennai October 2004
Iridium - $ consumption rate vs file size
0
2
4
6
8
10
0.01 0.1 1 10 100 1000
File size (kbyte)
Co
nsu
mp
tio
n r
ate
($/
kb
yte
)
Dial-up
SBD
DBCP Workshop, Chennai October 2004
SBD vs Dial Up
•SBD easy to SBD easy to
implement….implement….
•Cost penalty?Cost penalty?
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!$115k for 6 months!
DBCP Workshop, Chennai October 2004
Revisit dial-up!
• Charged at 1$/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
DBCP Workshop, Chennai October 2004
DBCP Workshop, Chennai October 2004
DBCP Workshop, Chennai October 2004
DBCP Workshop, Chennai October 2004
Impulse event – tilt record
DBCP Workshop, Chennai October 2004
DBCP Workshop, Chennai October 2004
DBCP Workshop, Chennai October 2004
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
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….
DBCP Workshop, Chennai October 2004
DBCP Workshop, Chennai October 2004
IRIDIUM