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Re: The saturation aspect on tdma transmission

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Ex Member
Ex Member

Apr 7th, 2009 at 12:03pm  
Please elaborate on your question.  

You certainly need to determine your BUC/SSPA requirement to close specific data/symbol rates.  TDMA or not, the BUC must be able to close the symbol rate of the upstream/return carrier it is operating in (without saturating/distorting).  For example:  A system operating in a 2048k upstream must be able to close the full 2048k return (and meet the UCP for the inroute group).

That is why a good 1dB compression test is necessary. 

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Eric Johnston
Senior Member

Posts: 2109
Reply #1 - Apr 7th, 2009 at 8:27pm  
I'll try to explain my question.

My colleague claims that if the BUC saturated it possibly be prevented  by moving the idirect to another inroute group with smaller symbol rate (for example- 3 times smaller).

If the hub has different inroute groups with different symbol rates but all using the same modulation and FEC then doing what is suggested will reduce the required BUC power by 3 times and probably enable it to be operated out of saturation, but at the penalty of reducing the customer bit rate to one third.

As far as i know the BUC will transmit exactly the same power and the only difference will be that the bursts will be spreaded on a larger frequency bandwidth.

If you leave the power, bit rate and FEC alone and alter the modulation BPSK - QPSK - 8PSK - 16QAM  the effect is as you describe, the bandwidth alters, the power spectral density alters and the power stays the same throughout. 

In both cases i'm talking on the same customer's upstream bit rate.
I don't think your colleage realised that the same bit rate was wanted.

what i'm trying  to say is that the entire tansmission power depends on the capacity that the idirect got from the provider and has no relation to the size of the upstream carrier.

Yes, the section of transponder leased, e.g. 1 MHz, has a specific entire maximum uplink power or earth station eirp allowed into it.  If, for example, this is equivalent to 4 watts from a 1.2m dish then you might use the 1 MHz for four TDMA carriers, one rated at 2 watts into 1.2m dish and using 500 kHz, and two others, each rated at 1 watt into 1.2m dish, each occupying 250 kHz.  Say 360 and 180 and 180 kbit/s data.

I hope this helps. It is bit complicated to explain briefly.

Best regards, Eric.
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