## Calculating Bandwidth

Bandwidth determines how fast a satellite broadband connection is. Knowing how much bandwidth a satellite operator and VSAT networks can offer is crucial in choosing the right satellite broadband plan for your business. Satellite Internet plans differ in terms of speed, availability and reach. Depending on the type of business you have and the frequency of Internet usage, you may want to consider a very high or average satellite bandwidth. Satellite operators, like traditional Internet service providers, only offer a limited amount of bandwidth.

Calculating the available bandwidth is so easy. Just sum up the bandwidth of each amplifier (transponder). Internet carriers usually have more than one carrier. Computing the bandwidth for each carrier is more complex as it differs from carrier to carrier. Here is an example of calculations you need to do in order to choose the right satellite carrier.

Compute the satellite carrier bandwidth by referring to the basic formula for carrier bandwidth: Symbol Rate (SR) = Data Rate (DR) / (modulation factor (m) x Viterbi FEC rate (CRv) x Reed Solomon FEC rate (CRrs)).

The value for “DR” should be the data rate of the carrier in Mbp/s (megabits per second). You can check DR on the carrier parameter sheet. The value represents the amount of data passed on the carrier. Another term for DR is information rate.

The modulation factor refers to the transmit scheme that decreases the bandwidth while still transmitting the data. There are various modulation schemes such as 16QAM, BPSK, 8PSK, QPSK and 8QAM. In reference to the above equation, you can use the following modulation factors: 16QAM = 4, 8QAM = 3, 8PSK = 3, BPSK = 1 and QPSK = 2. Check the carrier’s parameter sheet to know the modulation scheme.

The Viterbi Forward Error Correction (FEC) rate can be changed to add bits to the data stream, thus allowing for error correction. Common Viterbi FEC settings include 1/2, 2/3, 3/4 and 7/8. The first digit is the number of information bits, and the second one is the number of information bits plus added error correction bits. The setting can be found also in the carrier parameter sheet.

If Reed Solomon FEC is used, interchange 188/204 “CRrs” in the equation. This factor serves the same purpose as Viterbi FEC. But unlike Viterbi FEC, it is fixed. Reed Solomon FEC can either be on or off. This factor is also indicated on the satellite broadband carrier parameter sheet.

The details above may seem difficult to understand, that’s why at Best Marine Communications we do all this for you.