Instruction manual

9522B Iridium Satellite Modem

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6. Appendix A: Sample Data Transfer

Calculations

Note: The calculations below are based upon maximum

theoretical throughputs. Real world transmission times for

the Iridium Satellite Network have proven to be as much as

twice as slow.

When transmitting the data back from the station, the power

consumption of the modem must be taken into account in order

to avoid excessive discharge of the battery power supply. To get

an idea of what the transmission time and associated power

drain might be for a typical metrological station, consider the

following example:

A station measures wind-speed and direction, precipitation,

temperature and relative humidity, solar radiation, and

barometric pressure. The datalogger is a CR1000. The monthly

data file contains 2 data tables; a small maintenance table and a

30 parameter meteorological data table. The size of a monthly

ASCII data file is 124Kb.

If the station’s data were downloaded monthly, the time (T) for

the data transfer could be calculated as shown below:

(Download)

= File size (Kb) / Transfer Rate (72 Kb/min)

With a file size of 124 Kb and a transfer rate of 72 Kbytes per

minute, the download time is approximately 2 minutes.

If the data were downloaded daily, the file would be much

smaller, approximately 5KB. A daily data transfer time would be

approximately 5 seconds. Please note that a 4 to 15 second

connection time should be added to the above times to account

for the initial connection time.

Table 2 below shows the transfer time depending on whether

data is collected daily, weekly or monthly.

Collection Interval File size (Kbytes) Transfer time

Monthly 124 2 minutes

Weekly 35 30 seconds

Daily 5 5 seconds

Table 2: Data Transfer Time Estimates

The CR10X datalogger generates data arrays which are very

similar in size to the table-based dataloggers. For example the

station mentioned above generates a 124 Kb meteorological

data table and a 2 Kb maintenance table each month. If a

CR10X is employed to measure the same parameters the data

arrays would be the same size.