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VSAT technology and installation >> iDirect Forum: hubs and terminals >> downstream UPC

Message started by mike123 on Nov 26th, 2009 at 9:03am

Title: downstream UPC
Post by mike123 on Nov 26th, 2009 at 9:03am
Hi all,

iDirect's Uplink Control Process (UCP) can adjust changing weather attenuation through power adjustment on the upstream. However on downstream there is no such feature available.
I heard that usually an external UPC is used to compensate rain fade at the HUB's TX path.
Does anyone know how that works in detail? What hardware is used? I assume it is a done via an adjustable attenuator, but cannot find any details on the internet?

Can somebody point me into the right direction?

Thanks a lot, Mike.

Title: Re: downstream UPC
Post by Forum Admin on Nov 26th, 2009 at 11:52am
One (simplified) way to do uplink power control at the hub on the outlink downstream carrier:

You need a beacon receiver to measure the downlink path loss.
Compare with nominal and multiply by a numerical factor related to the downlink versus uplink frequency attenuations.
Apply the result to a variable attenuator in the uplink transmit path.

It sounds easy but is actually difficult and needs to be done with great caution and strict limits. There are considerable problems with calibration, tracking, equipment and cable gain drift with temperature, fast scintillation, step changes due to poor connectors, interference, sun noise, faults etc. Under no circumstances do you want the clear sky uplink power increasing spontaneously by 10dB due to some software interaction with an anomaly condition and overloading the satellite transponder.

Check with the satellite owner for rules that you must comply with regarding UPPC operation.

For equipment read here  Miteq UPPC D-218 as a typical example.

Best regards, Eric.

Title: Re: downstream UPC
Post by mike123 on Nov 26th, 2009 at 12:28pm
Thank's for the fast and comprehensive input, Eric.

Title: Re: downstream UPC
Post by TDMAMike on Nov 26th, 2009 at 1:15pm
Agree w/ Eric. UPC for the outbound (most larger earth stations/terminals are equipped with them).  

Title: Re: downstream UPC
Post by Agor on Nov 27th, 2009 at 7:39pm
Adding DVB-S2 ACM is even better, as it takes care for the remote terminal's reception in rain conditions, etc.

Title: Re: downstream UPC
Post by Scout on Dec 2nd, 2009 at 9:58pm
Using the ACM capability on iDirect is a great feature, but I think it's important to keep the two as separate concerns.
the UPC on the hub should be controlled separately from the ACM feature.  If you use the ACM to compensate for all hub side fade, then given a scenario of a severe fade hub side, all remotes would end up using the worst MODCOD (modulation and coding) this would be very inefficient.  
If you implement the correct hub power control using external devices, you maintain the benefits of ACM by having it relate to individual remotes receive performance rather than the hub Tx performance.  ACM was not designed to compensate for lack of UPC at a hub location.
Although a solution of sorts, I think it would be far more beneficial and efficient to utilize the correct UPC hub side.
Just my 2 cents.

Title: Re: downstream UPC
Post by Agor on Dec 3rd, 2009 at 2:01pm
I agree. I suggested to add ACM, not to use ACM instead of UPC.



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