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https://www.satsig.net/cgi-bin/yabb/YaBB.pl VSAT technology and installation >> iDirect Forum: hubs and terminals >> Occupied Bandwidth https://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1221227869 Message started by wow on Sep 12^th, 2008 at 2:57pm

Title: Occupied Bandwidth
Post by wow on Sep 12^th, 2008 at 2:57pm

what is this Occupied Bandwidth in iBuilder? Is this the real bandwidth that it is going to occupied in the satellite bandwidth ?

How do we calculate the bandwidth when using the spread spectrum?

Title: Re: Occupied Bandwidth
Post by TDMAMike on Sep 13^th, 2008 at 2:09am

Occupied BW is the actual MHz you are occupying on the Xponder. If you change your symbol, info or transmission rate you can change that value in iBuilder. You can also change it if you change your modulation scheme.

Title: Re: Occupied Bandwidth
Post by wow on Sep 13^th, 2008 at 6:17pm

Hi Mike,

thanks for the info.

Do you have the calculation sheet or formula for the info rate, tx rate, FEC, modulation, Spread Spectrum factors?
So with these factors input, i can calculate out the bandwidth required.

regards,
w

Title: Re: Occupied Bandwidth
Post by TDMAMike on Sep 13^th, 2008 at 9:25pm

Do you have access to iDirects iNPT 8? It is on the TAC website.

Title: Re: Occupied Bandwidth
Post by wow on Sep 14^th, 2008 at 4:00pm

yes. I will try that.

thanks.

regards.
w

Title: Re: Occupied Bandwidth
Post by jtfly on Oct 15^th, 2008 at 9:21pm

When using SS, an SF of 1 (or SF=1 which increases the unique word size which helps your remote stay locked) will give you no spreading and your occupied bandwidth will not change. Once you change go SF=2 your occ bw will be doubled and SF=4 will quadruple your occ bw. So a 256k data rate, 1.2 spacing, 1/2 BPSK, SF=4 will run you near 2.5MHz of occ bw.

Title: Re: Occupied Bandwidth
Post by wow on Oct 16^th, 2008 at 7:48am

Hi,

that is the problem with spread spectrum...a lot of bandwidth is needed.

By the way can iDirect implement this 1/2 BPSK?

Regards,
w0w

Title: Re: Occupied Bandwidth
Post by jtfly on Oct 21^st, 2008 at 2:08pm

On the upstream it supports BPSK / .431 FEC and the downstream supports BPSK .431 or .49 FEC. Spreading is only available with BPSK modulation.

Title: Re: Occupied Bandwidth
Post by TDMAMike on Oct 22^nd, 2008 at 11:42am

If you are in the market to do spread spectrum then you more than likely have enough money to support the MHz required (if not you probably should be doing it to start with).

The main reason to use spread is to minimize PSD with the smaller apertures commonly found on moving platforms.