By Dave Suffys, Sales Support Manager at Newtec.
Blast to the Past
Let’s go back in time…to DVB, Digital Video Broadcasting, a standard created with a single application in mind: video. It was created because the consumption of video was increasing and it was quickly becoming a successful business model with more and more people enjoying watching television.
Initially these DVB-S transmissions used a single carrier coming from a single modulator over a single transponder. Millions of paying subscribers were/are reached with this DVB-S standard and there are still new DVB-S services launched as we speak, you might have read about it in the press. Even so that we have fine-tuned our Equalink® predistortion so that it provides gain, even in DVB-S.
The Evolution of DVB
Fast forward to the evolution towards DVB-S2, the new standard still included “video”, but also other emerging applications, such as data over satellite. I sometimes refer to DVB-S2 as Digital Versatile Broadcasting, similar to the “V“ in DVD, because of this.
Adaptive Coding Modulation (ACM) and multistream capabilities made this standard ideally suited for data applications. Many networks, regardless of vendor, employed and still employ DVB-S2 in the forward link in order to take advantage of its data capabilities and superior performance over other modulation techniques.
Unfortunately, after much progress, the industry laid dormant for years after this with many people predicting that DVB-S2 would in fact be the last standard. Some were even saying “we are very close to the Shannon limit now” thinking that no further improvements could be made. (“Shannon” referring to the Shannon-Hartley theorem that calculates the maximum rate of which information can be transmitted over a communications channel).
However, some bright minds still thought improvements were possible. They believed it was just a matter of creating enough of an improvement to justify the hassle of implementing yet another new standard. They were right and after a fruitful cooperation among all industry players a “new” standard was born – DVB-S2X. Well, technically speaking, an extension to the existing standard (hence the “X”).
The “New “Standard
There are a number of upgrades which justify the extension, including additional MODCODs for linear (multi-carrier) operation. The original DVB-S (and DVB-S2) standard was created with full transponders in mind; so, for non-linear operation.
But for linear (multi-carrier) operation, the constellation diagram is tuned specifically for this mode, resulting in extra MODCODs that provide gain.
Also in the DVB-S2 standard there are some MODCODs that require a big jump (in dBs) to reach the next one. With DVB-S2X these "gaps" have been filled in with additional MODCODs resulting in "jumps" that are evenly spread out with a distance of on average 0.5 dB.
Is this a gain? Yes, this can be called a quantization gain. The most important thing for me is that it takes away some frustration when designing links or doing system design. In the past I bitterly remember needing to put up a fight when I wanted to use just 16APSK. Fortunately with ACM, a link will simply use the highest MODCOD that is possible. The result is that we now have a couple of links that were budgeted to run 8PSK that are now happily running 32APSK.
So the exact same thing is going to happen with 64APSK and 256APSK with the new DVB-S2X: people will be running those MODCODs before they actually realize it themselves. We know that current and upcoming satellites are getting more powerful by the day; so I say "bring on the 64APSK and even the 256APSK!". In fact we’ll be making some results of a 256APSK link public soon at this blog, so be sure to return to see our findings.
Lastly, in this extension to the DVB-S2 standard, there are some fundamental techniques that will be used in new applications in the near future such as spread spectrum, channel bondging and a few other nifty techniques. So, fun times are ahead, even though we still have a couple of challenges to tackle.
I will never again say that a standard is “the last standard”.
Visit Newtec’s website to Download the DVB-S2X Calculator. It's a free tool. After registering, you can choose from two training options to learn more about the tool.
Share your thoughts via the comment box or send me a private message in case of questions (use email@example.com).
Sales Support Manager