# A bit of satellite technology

As mentioned here, I work in the satellite industry. I am pretty new to it and everyday is a learning experience. Today, I sat down with our in house satellite guru and found out how one calculates the bandwidth occupied by a carrier from the from the data rate on a satellite link. The formula is

 BWAL = (Sr*1.4)

Where
BWAL = Bandwidth allocated for the satellite link in Khz.
Sr = Symbolrate of the link in Ksym/s (Kilo Symbols per second).

Sr in turn is calculated using the following formula

 Sr = Dr*(1/MI)*(1/FEC)*(1/RS)

Where
Dr = Datarate in Kbps.
MI = Modulation Index (The values of MI for the different modulations are BPSK=1 | QPSK = 2 | 8PSK = 3 | 16PSK=4 | 16QAM = 4).
FEC = Forward Error Correction.
RS = Reed Solomon value. This can vary depending on what values are being used. Reed Solomon is an external codec as compared to Turbo which is a stand alone codec. If RS is not being used in the link, then a value of 1 is used.

Pretty confusing eh :). As if though this is not enough, there is another value called Information rate (Ir). And the formula for that is

 Ir = Dr(1/RS)

Think that is enough satellite technology for one day :).