PNG : A new CTD profiling float IRIDIUM - some results Christian GAC and Sylvie LE BRAS Ifremer - TMSI-TSI-ME
Iridium Features 66+ satellites in low earth orbit Designed for voice communications Real-time: inter-satellite communications 2-way link True global Compact antenna Future assured
Iridium constellation
Performance assessment of the Iridium modem Tests carried out by using the CDM9500I35-IG Iridium modems from Nal Research Corporation The module provided with : GPS for positioning. RS 232 hardware interface AT commands Performance tests by using 1 - Z-MODEM protocol 2 - FTP protocol 3 - TFTP protocol
Performance assessment of the Iridium modem Iridium satellite Network Iridium Modem Terrestrial station of reception. Telephone Network IFREMER Network
Transmission data rate Some tests of file transfer (ftp) of 12 Kbytes were carried out 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
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 No reply / Configuration problem Transmission (12KBytes) 85s 140s 92.8s Unknown host Reception (100 bytes) 3s 6s 4.6s -- disconnecting 42s 45s 43.7s --
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.
Connecting mode Transmission mode www.ifremer.fr Power consumption Initialisation Disconnecting mode
Power consumption Timing minimal maximal averaged Hourly consumption Initialisation (15s) 1.7 mah 2 mah 1.9 mah 456mA disconnecting mode (22s) 2.46 mah 2.8 mah 2.49 mah 300 ma Connection (18.5s) 9.38 mah 10.1 mah 9.8 mah 734 ma Connecting mode (30s) 6.11 mah 6.24 mah 6.18 mah 741 ma Transmission (93s) 31.62 mah 36.55 mah 33.8 mah 1296 ma Reception (5s) 0.87 mah 1.17 mah 0.99 mah 720 ma disconnecting (44s) 7.8 mah 8.9 mah 8.65mA.h 711mA A whole transmission (i.e.: initialization + connection + transmission + reception + disconnection) thus consumes averaged 63.8 mah.
Number of attempts necessary Connection n 1 2 3 4 5 6 7 8 9 10 11 12 13 Attempts necessary 4 2 1 2 1 2 3 1 3 2 1 4 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 IRIDIUM ARGOS Number of satellites 66 (6 orbits of 11 satellites) 7 (1 equipped with a downlink) Terrestrial cover Continuously total Total but periodic 15% of time Data rate 132 bits/s 400 bits/s Mode full-duplex transmission No downlink Dimensions (cm) 24.1 X 7.2 X 3.8 12 X 4.5 X 2 Mass 580 g 200 g Connection RS 232 RS 232 Kbyte power consumption 23 mwh /Kbyte 64 mwh /Kbytes Cycle power consumption 276 mwh/cycle 768 mwh /cycle Transmission frequency 1616 1626.5 MHz 401.65 MHz Integration easiness hardware : yes yes software : needs to be realized a protocol Modem cost $ 1,200 < $ 1,000 Antenna cost $ 1,140 $ 250
Conclusions Instrument will be able to call Interactive control of new floats (real time needed?) by 2 way communication Future trends : GPS positionning Evaluation possibility of a new protocol by AT commands Higher data volume can be easily improved by using any protocol
Near future tests Performance assessment of a new antenna from Webb Research Corporation. Needs to use a coupler for matching IRIDIUM and GPS outputs. Beam pattern measurement Communication transmission (power consumption, real baud rate, etc) Pressure improvement Repeat transmission : minimum time delay?
Test of a combined Iridium GPS Antenna
Near future tests Protocol matched to profiling float Between 4 Kbytes and 48 Kbytes file size for transmission 100 bytes file size for reception Necessity of an acknowledgment message? Performance assessment of some other Iridium functionality s : access direct service with Internet (the modem must be connected to the PC by a 9 wires link) the SMS (Shorts Message Service). The procedure of these tests remains to be defined. Software implementation to our electronic card Instrument parameters to update remotely