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VSAT technology and installation >> iDirect Forum: hubs and terminals >> Timeslots

Message started by xenogears on Feb 9th, 2011 at 11:09pm

Title: Timeslots
Post by xenogears on Feb 9th, 2011 at 11:09pm

We have an Inbound 600 Kbps QPSK 2/3 with 19 traffic slots.
Now, we are going to 1000Kbps with BPSK 2/3 But I don't
know how to calculate how many traffic slots we'll have.

Someone knows how to do that?

Best regards

Title: Re: Timeslots
Post by dot on Feb 10th, 2011 at 9:07am
You would use iNPT to do the calculations. But a 600 Kbps information rate carrier running QPSK TPC 0.66 gives you about 100 timeslots, not sure where you get 19 from?

Title: Re: Timeslots
Post by xenogears on Feb 11th, 2011 at 7:36pm
Simply, it's the config given by iBUILDER!

We have: QPSK 2D-16S-438bytes (2/3)
Information rate: 600 kbps
Timeplan parameters:
Acquisition aperture: 773
Guard band: 8
Traffic slots: 19

By the way, what's iNPT and where can I find that?

Title: Re: Timeslots
Post by dot on Feb 12th, 2011 at 9:37am
aha, 2D-16state and not TPC. That makes the difference. Yes this configuration does have only 19 slots because the FEC block is 438 bytes long or 3.5 kilobits.

You cannot run that FEC with BPSK because its not supported and hence I cant tell you how many traffic slots there will be. What are you trying to achieve by changing the modulation and coding? The QPSK carrier has a target Eb/No of 3.8 dB while the BPSK you want to move to has 4.2 dB for a 100B2/3 equivalent and carries a lot less traffic.

You can contact your iDirect sales engineer for a copy of iNPT and training on how to use it. Search for iDirect network design classes also.

Title: Re: Timeslots
Post by xenogears on Feb 15th, 2011 at 6:34pm
Yes, BPSK 2D-16S-100B-1/2 works with Evolution linecard.
Our problem is that we have a remote very far, with 7dB less than the center of the beam.
The Tx margin power is less than 8dB so we have to put this remote alone in an Inbound of 600 Kbps!

In fact, we have a very old antenna (> 45 years old) with a tired satellite (IS 701) that should be change in august.
But right now, we have to do something for our customers.
We have 7 MHz that we can use freely so I'm looking for a way to enlarge the bandwidth whithout a loss of SNR.

Title: Re: Timeslots
Post by dot on Feb 16th, 2011 at 1:49pm
So you are actually wanting to improve your Eb/No performance?

Your QPSK 2D-16S-438bytes (2/3) carrier has 19 traffic slots and requires an Eb/No of 3.8 dB and uses about 541 Khz.

A possible solution might be QPSK 2D-16S-170B (1/2) at 3.6 dB, where a 600 Kbps info rate carrier requires 740 KHz and provides 51 timeslots. The reason for more timeslots is due to 170 byte FEC blocks.

The only better Eb/No performance you will get is if you start spreading.

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