Performance assessment of the Iridium modem
The aim consists in working with a new communication system using a satellite constellation,
Iridium, which allows a whole continuous cover. The tests were carried out on the
CDM9500I35-IG Iridium modems dedicated to the data transmission. The module was
installed on the roof of a building and not at sea. The module is provided with a GPS for
positioning. GPS position is obtained one minute after the modem is powered on.
Synoptic of Iridium working with the Ifremer network
Iridium
satellite
Network
Iridium
Modem
Terrestrial
station of
reception.
Telephone
Network
Transmission data rate
In this test, the Iridium modem sends 100 data packages of 100 bytes in PPP.
100 packages of 36 bytes:
Protocol [ip]:
Target IP address: 134.246.150.1
Sending 100, 36-byte ICMP Echos to 134.246.150.1, timeout is 4 seconds:
Success rate is 100 percent (100/100), round-trip min/avg/max = 1364/1547/3924 ms
100 packages of 100 bytes :
Protocol [ip]:
Target IP address: 134.246.150.1
Sending 100, 100-byte ICMP Echos to 134.246.150.1, timeout is 8 seconds:
Success rate is 100 percent (100/100), round-trip min/avg/max = 2288/2432/4764 ms
Some tests of file transfer (ftp) of 12 Kbytes were carried out too.
Test of put (transmission) with 2400b/s
12288 bytes in 56 s; 1755 bits/s
Test of get (reception)
100 bytes in less than 1s; >800 bits/s
IFREMER
Network
Connection timing
The following table describes typical connection timing:
Connection timing
Minimal time Maximal time Averaged time
failure cause
Numbering
13s
18s
15.3s
Busy, engaged
User’s statement
Checking
20s
23s
22s
--
Connecting
45s
52s
48.4s
Transmission (12KBytes)
85s
140s
92.8s
Reception (100 bytes)
3s
6s
4.6s
--
disconnecting
42s
45s
43.7s
--
No reply /
Configuration problem
Unknown host
The following timing describes the table above.
Initialisation
Network connecting
Transmission
Reception
40 s
48 s
92 s
4s
230 mA with a 1.4A
peak
850 mA averaged with a
1.4 A peak
1.1 A
0.8 A
Real transmission data rate
The transmission time can vary between 50 and 90 seconds for a 12 Kbytes file. That yields to
a minimal data rate of 132 bytes/s for a transmission.
Power consumption
minimal
maximal
averaged
Hourly
consumption
1.7 mAh
2.46 mAh
9.38 mAh
6.11 mAh
31.62 mAh
0.87 mAh
7.8 mAh
2 mAh
2.8 mAh
10.1 mAh
6.24 mAh
36.55 mAh
1.17 mAh
8.9 mAh
1.9 mAh
2.49 mAh
9.8 mAh
6.18 mAh
33.8 mAh
0.99 mAh
8.65mA.h
456mA
300 mA
734 mA
741 mA
1296 mA
720 mA
711mA
Timing
Initialisation (15s)
disconnecting mode (22s)
Connection (18.5s)
Connecting mode (30s)
Transmission
(93s)
Reception (5s)
disconnecting (44s)
A whole transmission (i.e.: initialization + connection + transmission + reception +
disconnection) thus consumes averaged 63.8mAH.
Number of attempts necessary
The table below establishes that the connection is not always set at the 1st test.
Connection n°
Attempts
necessary
1
4
2
2
3
1
4
2
5
1
6
2
7
3
8
1
9
3
10
2
11
1
12
4
13
2
Generally, the number of test remains lower than 4, and the errors are because of a busy
connection, or a problem of not-recognition of the configuration. These errors are thus not
really rectifiable. However, they require starting the procedure again. One thus needs on
average 2.1 attempts before a connection success. Generally, if the connection is not
established at the first attempt, it is preferable to wait a few minutes before trying the test
again.
Other connections requiring more than 10 attempts provided a second phenomenon,
unsystematic. Thus, if a connection is started again without powered the supply off, and then
the modem can not answer.
Day's time range
About the studied "day's time range", middle of morning, middle of afternoon, it does not
seem that there is some distinguished changes, as for the connection quality. Maybe the
slightly best moment is in the morning. However, other time slots can be better.
Connection failure
According to the French operator “France Telecom”, the problems of connection are assigned
to the Iridium system. A software is currently under development to improve mails messages,
but at the moment there is nothing of designed to improve the data transmission.
Furthermore, in case of communications requiring several satellites, some of them can be out
of order. That can explain the difficulty to establish a connection at the first test.
Table of comparison between Argos and Iridium
Number of satellites
Terrestrial cover
Data rate
Mode
Dimensions (cm)
Mass
Connection
Averaged power consumption
Kbyte power consumption
Connection power consumption
Transmission frequency
Integration easiness
Modem cost
Communication cost
Antenna cost
IRIDIUM
ARGOS
66 (6 orbits of 11 satellites)
Continuously total
2400 bits/s
full-duplex transmission
24.1 X 7.2 X 3.8
580 g
RS 232
750 mW
5.6 mWh /Kbyte
 2.8 mWh/connection
1616 – 1626.5 MHz
hardware : yes
software : needs to realize a protocol
$ 1,000
7 (1 equipped with a downlink)
Total but periodic 15% of time
400 bits/s
No downlink
12 X 4.5 X 2
200 g
RS 232
128 mW
1.4 mWh /Kbytes
 0.7 mWh /connection
401.65 MHz
$ 1/minute
$ 1,000
yes
< $ 1,000
annual contract, fixed price
3280 € /float /year
$ 210
This table includes the GPS integrated in the 9500 Iridium modem. A new modem (9505) is
also available with small overall dimensions of 30% and a reduced consumption of 5%.