====== Iridium Toolkit ======

On [[https://github.com/muccc/iridium-toolkit|GitHub]]


===== Frame Format =====

==== Frame Header ====
All (parsed) frames start with a header:
<code>IRA: i-1472473197-t1 000001626 1627088000  97%   0.009 129 DL</code>

^Field Number^Content^Example^Comment^
|0|Frame type|IRA:| |
|1|UNIX timestamp in seconds when the recording started|i-1472473197-t1| The i- prefix and -t1 suffix a historical artefact...|
|2|Time in milliseconds inside the recording|000001626| |
|3|Frequency in Hertz|1627088000|Estimated center frequency|
|4|Confidence in percent|97%|Confidence is estimated during demodulation by gr-iridium|
|5|Signal level|0.009|Arbitrary scale|
|6|Length in symbols|129|Excluding the 12 symbol sync word. One symbol equals two bits|
|7|Direction|DL|DL or UL|


==== IRA: Ring Alert ====
Ring alerts are sent periodically by the satellite to every spot beam. Every 90 ms a new ring alert gets sent to another spot beam. There are 48 spot beams, so every 4.32 s a ring alert is sent to the same spot beam.

Example:
<code>IRA: i-1472473197-t1 000002706 1627087872  97%   0.012 132 DL sat:81 beam:20 pos=(+46.64/-115.08) alt=791 RAI:48 ?00 bc_sb:07 PAGE(tmsi:0ca5b2e2 msc_id:01) PAGE(NONE)</code>

^Field Number^Content^Example^Comment^
|8|Satellite number|sat:81|7 bit field|
|9|Spot beam number|beam:20| |
|10|Satellite or spot beam position|pos=(+46.64/-115.08)| |
|11|Satellite or spot beam altitude|alt=791 |In km|
|12|Ring alert interval|RAI:48| Always 48 in the live system|
|13|Unknown|?00| |
|14|Broadcast channel sub-band|bc_sb:07|Brodcast channel for the spot beam is in this sub-band|
|15-|TMSI pages|PAGE(tmsi:0ca5b2e2 msc_id:01) PAGE(NONE)|A NONE page signifies the end of the list of pages|

As there can be a different amount of pages, the size of a ring alert frame is not constant.

=== Location Information ===
The ring alert contains two different, alternating, locations:
== SV Location ==
Locations with a high altitude (e.g. > 100 km) can be treated as as the location of the SV (Space Vehicle).

== Spot Beam Location ==
Locations with a low altitude (e.g. < 10 km) can be treated as the location where the SV thinks that the particular spot beam is hitting the earth’s surface. Note that this is not the location of a subscriber.