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HX Rate Code

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Jan 10th, 2008 at 12:52am  
Hi Eric,

I think you can answer my query. I need to know outbound and inbound rate code value of hx? How much did you get it with 96 signal?

Many thanks and happy new year...2008!!

With Regards,

Javid
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Eric Johnston
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Reply #1 - Jan 10th, 2008 at 9:26am  
The DVB-S2 outlink carrier can have a variety of modulation and FEC code rates: Encoding DVB-S2: BCH with LDPC 3/5, 2/3, 3/4, 5/6, 8/9, or 9/10 (8PSK) 1/2, 3/5, 2/3, 4/5, 5/6, 8/9, 9/10 (QPSK)

The remote site uplinks have 4 alternative FEC code rates.  Transmit encoding: Rate 1/2, 2/3, 4/5 TurboCode, Rate 1/2 Convolutional

The FEC code rates are varied dynamically so as to optimise the link.  In clear sky, I was getting 8/9 8-PSK on the outlink and 4/5 Turbo on transmit. 

Best regards, Eric.
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James-BW
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Reply #2 - Jan 10th, 2008 at 9:48am  
Hi,

In response to Erics update, the optimum values  8/9 8-PSK Recieve and 4/5 on Transmit.   

Regards,

James
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Reply #3 - Jan 10th, 2008 at 9:47pm  
Hi James/Eirc,

Thank you for your reply.

I'm getting 8PSK 8/9 (16) and 256k 4/5. Is there any way i can increase transmit encoding from 256k 4/5 to 512k 4/5?


Many Thanks,

With Regards,

Jaweed PAtel
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Reply #4 - Jan 10th, 2008 at 10:30pm  
Quote:
Is there any way i can increase transmit encoding from 256k 4/5 to 512k 4/5?
The 256k and 512k parts are symbol rates. The 4/5 represents coding. So going from 256k 4/5 to 512k 4/5 is not a transmit encoding change, it's a transmit symbol rate change.

The answer to your question depends primarily upon the size/efficiency of your parabola, the transmitter wattage, your satellite/transponder assignment, and your location on the ground. Sometimes a larger dish or a bigger transmitter is the answer. Other times it's a matter of resolving existing installation issues.

//greg//
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Eric Johnston
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Reply #5 - Jan 11th, 2008 at 8:59am  
To double the uplink data rate you need a dish of twice the area or twice as much actual adjusted transmit power.

The 256kps uplink is shared with many other sites, so your transmitter is ON only intermittently to transmit a short burst.  A way of increasing your uplink capacity, during congested periods, may be to choose a higher tariff so you are given a corresponding greater proportion of the time slots available.  If you wanted dedicated 256ksps continuous on your uplink I guess BW could provide that but they would have to buy a dedicated hub demodulator for you and the charge for the uplink satellite capacity would be very many times the shared rate - but you get what you pay for.

The HX50 modem is able to transmit bursts at 128, 256, 512 and 1024 ksps.    The HX100 modem goes up to 2048 ksps.

Best regards, Eric.
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« Last Edit: Jan 11th, 2008 at 2:17pm by Eric Johnston »  
 
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Reply #6 - Jan 11th, 2008 at 12:16pm  
Eric Johnston wrote on Jan 11th, 2008 at 8:59am:
The HX50 modem is able to transmit bursts at 128, 256, 512 and 1024 ksps.
If you take a second look at the HX50 modem specs Eric, you'll see those numbers represent symbol rates (ksps). I saw Hughes first use this practice with the DW7000 spec sheet. In the case of the HX50 specifically, they publish a transmit information rate (data rate) of "up to" 3.2 Mbps and transmit symbol rates of 128, 256, 512 and 1024 ksps

//greg//
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« Last Edit: Mar 2nd, 2008 at 9:52pm by Admin1 »  

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Reply #7 - Jan 12th, 2008 at 7:17pm  
Acknowledged. What I was suggesting in the phrase "I saw Hughes first use this practice  " meant to imply that they're using slight-of-hand numbers on their spec sheets. Only those folks like us who've "been there - done that" can actually see through the inflated specifications to actually consider the true underlying performance potential

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Reply #8 - Mar 2nd, 2008 at 8:42pm  
Hi folks,

"I don't quite understand the 3.2 Mbps figure as that far exceeds the tx data rate of the HX100 modem (max 2 Msps or 1638 kbps at 4/5 FEC). "

Hughes is not making up these numbers in the spec sheets.

3.2 Mbps = 2 Msps @ 4/5 Fec ...

The HX100 terminals  will work with 2 msps inbound carriers. The HX50 will work upto 1.6mbps (ie 1 msps @4/5 fec).

Cheers.
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Reply #9 - Mar 2nd, 2008 at 9:58pm  
Thanks, I think I have worked out what is going on, the modulation is OQPSK with 2 bits per symbol.

The HX100 modem has a max 2 Msps transmit rate.
Transmit encoding: Rate 1/2, 2/3, 4/5 TurboCode or Rate 1/2 Convolutional.  Assume 4/ Turbo OQPSK
Transmission bit rate = 4 Mbit/s (2 bits per symbol)
Information bit rate = 4/5 * 4 Mbit/s = 3.2 Mbit/s.

It all then makes sense.

Best regards, Eric.
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