8PSK-Turbo Code
- Thread starter danknapp76
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8PSK is a modulation scheme. It essentially allows more data per symbol to be modulated. In standard QPSK, 2 bits per symbol, in standard 8PSK it's 3, so that's a 50% gain on Dish's part.
DVB-S2 would be the encoding scheme and utilized MPEG4. 8PSK is simply how they modulate the satellite signal at Ku-Band down to your receiver. The DVB-S2 is embedded into the 8PSK modulated signal.
So whats the ultimate difference between Dish Network MPEG4HD Plug Turbo 8PSK when compaired to DirecTV MPEG4HD DVB-S2?
I am not seeing any reall difference here unless I am missing something.
I am not seeing any reall difference here unless I am missing something.
Got to love techies and how they know this and how planned to use this with MPEG4 to allow Dish to leapfrog Direct (read the article Scott; great once again!)
Here is a theory: If the techies with all their know how also ran the legal department at Dish wow what a major turn around there would be on all these lawsuits!
Here is a theory: If the techies with all their know how also ran the legal department at Dish wow what a major turn around there would be on all these lawsuits!
Here's better info on the 8PSK Turbo code:
Broadcom's Advanced Satellite Communications Technology Selected By EchoStar's DISH Network Service
Broadcom's Advanced Satellite Communications Technology Selected By EchoStar's DISH Network Service
So bottom line is 8PSK might not be as unique to dish as they'd have us believe...
I have been feverishly searching the internet and I think it is not if you choose to implement it or not; it may be possible that the technology is now on the new Direct Satellites and when operational, they can do the same; or I am wrong
They're the only one using Turbo coded 8PSK in the US. I'm not sure anyone else is using it overseas either. They're using DVB-S2 8PSK.
Now the Broadcom chipset in that Dish uses has the ability to tune the DirecTV DSS signals along with the DCII signals.
From what I understood from the past... Turbo coding is an advanced form of forward error correction. It allows you to get better performance and use less bits for FEC of the signal thus giving more bits for bandwidth. So turbo coded FEC 5/6 takes less bits than standard 5/6 FEC (or 2/3, etc) So a more data and less error correcting bits needed.
8PSK does not affect the satellite. DIRECTV could choose to turn it on their satellites if they wanted to do so.
8PSK as mentioned above is 3 bits per symbol 4PSK or QPSK is 2 bits/symbol. But since the symbol is more complicated (it can be in 8 different states rather than 4) it is harder for the receiver to figure out which symbol is being trasmitted. This comes into play with interference like rainfade. This is why Dish used 2/3 FEC with 8PSK and 5/6 with QPSK. This means that for 8PSK 1/3 of the bits are used for error correction and with QPSK they use 1/6, or 2x the error correction. This makes 8PSK only 35% or so more bandwidth rather than a simple 50% more.
DIRECTV uses Ka frequencies. They are much more succeptible to rain fade. Making it much more likely that 8PSK would fade out. The can compensate in 2 ways. One is to use more transmission power (which is limited by the satellite), another is to increase the amount of error correction to compensate.
Another consideration is that the receivers need to have 8PSK decoding hardware in them.
Dish elected to have all the HD in 8PSK since they upgraded the 6000 with the 8PSK module. Dish uses Ku frequencies, less succeptible to rain fade. Dish also has gone with a very conservative 2/3 FEC. 2/3 FEC Turbo encoded 8PSK has been shown to have less rainfade than 5/6 QPSK non turbo encode (I do not have a link to the study by some NASA scientist studying various encoding methods, but it was a very interesting paper but had a lot of equasions).
Essentially each provider has picked an encoding solution that they think is best. Dish, more limited by bandwidth, but having better spectrum for rain fade picked to go with 8PSK. DIRECTV has a ton of Ka bandwidth (each Ka slot has up to 2x the spectrum of a Ku slot (1GHZ vs 500MHZ)) elected to stay with QPSK.
Broadcom's 8PSK turbo code FEC (foward error correction) "increases information throughput by 35 percent over QPSK. 8psk Turbo Code 2/3 FEC add's about 10% data throughput over 8psk Viterbi RS 2/3 FEC. For E*, that means going from 39.6 Msp/s to 43 Msp/s per transponder giving them 7 HD Channels @ 6.15 Msp/s each.
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Adding technical details:
BCM4500 cannot support SR eq or higher then 30000 Ksps, that's why Dish set SR eq 21.5 Msps for all TC 8PSK tpns,
but DTV using 30 Msps with LG tuner for Ka tpns successfully.
BCM4500 cannot support SR eq or higher then 30000 Ksps, that's why Dish set SR eq 21.5 Msps for all TC 8PSK tpns,
but DTV using 30 Msps with LG tuner for Ka tpns successfully.
Thanks for not confusing the issue with rain fade which is a function of customer's rain rate zone and the amount of fade margin (Eb/No) above the threshold for the desired BER.
FYI - that press release is 4 1/2 years old !
I believe they have been using at least that long. First supported with the add on module for the 6000.
