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rick merritt
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Re: Issued Patents
rick merritt   12/18/2013 10:55:19 PM
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@dt_hayden: Thanks for links to the patents.

I'd love commentary on them from any astute comms EEs out there.

paragdighe
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SNR GAP
paragdighe   12/19/2013 5:00:39 AM
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The SNR gap to shannon capacity for QAM is ~9.5 dB @ 1e-7 probablity of error.

Lots of literature and links on this. 

http://www.stanford.edu/group/cioffi/ee379a/handouts/pamqam2.pdf

Today's codes achieve very close to this (I have heard). So coding+QAM4096~=capacity. So would be interesting to see which way this company goes especially if you decide to toss the popular OFDM-QAM combination. Who would want them for 1-2 dB improvement ?

 

Parag

paragdighe
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Re: SNR GAP
paragdighe   12/19/2013 5:12:50 AM
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I guess the catch is that QAM 4096 may be near impossible to implement taking into account the practical implementation issues (EVM etc etc). I think the benefit must be that Magnacom has a scheme theoretically almost equivalent to coded QAM4096. Thats a big deal.

Sheetal.Pandey
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Re: SNR GAP
Sheetal.Pandey   12/19/2013 2:17:43 PM
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well every battle in telecom industry is linked to bandwdth, if there s a breakthrough it will be a new revolutons for the technology.

sridhar.ramesh
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Re: Modulation marches forward
sridhar.ramesh   12/19/2013 4:11:27 PM
4K QAM is 12 bits per symbol without coding - simply log2(4096).

The 10 dB signaling advantage to 2 X power or spectrum advantage to 4X distance advantage referenced in this article don't sit well with each other.

Bert22306
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Re: Issued Patents
Bert22306   12/19/2013 4:13:23 PM
All we need is results.

For comparison, the US digital TV standard requires about 15.1 dB of SNR to achieve reception, in a gaussian channel. US DTV uses channel bandwidth of 5.3 MHz (and guard bands that bring this up to the 6 MHz channel width), and a net capacity of 19.29 Mb/s. The Shannon limit for a 5.3 MHz channel carrying 19.3 Mb/s is 10.6 dB of SNR minimum, required.

So this now-20-year-old standard is already only 4.5 dB from the Shannon limit. Unless Shannon's limit can be proved to have been violated, there ain't any 10 dB gains to be had here.

DVB-T2, the new European DTV standard, gets even closer. Last time I checked, it was ~ 3 dB from the Shannon limit.

So, all of this tells me that we're not looking at any "breakthrough in modulation." We're looking at refinements, much like DVB-T2 refined DVB-T1. Marginally better FEC codes, clever tricks on twisting the constellation, better interleaving, and so on. Small improvements that provide a small but measurable improvement.

Also, a significant point here. The purpose of OFDM is NOT to improve spectral efficiency. It is to improve resistance to multipath distortions. There's no such thing as a free lunch. What you pay, with OFDM, is moving away from the Shannon limit. So if a new modulation standard goes back to a single carrier approach, with improved equalizers, no one should be surprised. Equalizers benefit from Moore's law, after all. They are bound to improve over the decades.

y_sasaki
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Re: Modulation marches forward
y_sasaki   12/19/2013 4:32:02 PM
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Thanks. You are right, 4096QAM is 64x64 constallation, 2^6 x 2^6 = 12bit/symbol. I also wrote "Friis equasion" instaed of Shannon... Maybe because I often refer to both equasions to verify "revolutionaly communication method" on news :-)

y_sasaki
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Re: Modulation marches forward
y_sasaki   12/19/2013 4:46:49 PM
@ick merritt,

I personally believe 11ac 256QAM is already pushing little bit too far.

As Shannon's equasion (C=Blog2(1+S/N) suggests, the straightforward way to increase datarate (C) is to use more bandwidth (B). This was tried and failed on UWB (initially 500MHz/channel, hoped more than 5GHz/channel for future), partly applied to 11ac (up to 160MHz/channel).

Using higher frequency natunally increase bandwidth/channel, so there is high hope we can achieve more than 1Gbps datarate at 60GHz freq (802.11ad), however its laser-beam like characteristics and extremely low penetoration capability (you only can use 60GHz in clear line-of-sight) will limit is application.

MIMO is another way to increase datarate, but more than 4x4 MIMO will be impractical, since we need set of antenna / receiver / transmitter for each stream.

 

My most honest answer to "how we can get more datarate?" is "use wire!" :-)

BOMBOVA
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Re: Modulation marches forward
BOMBOVA   12/21/2013 12:03:15 PM
n Physics, gets streached,    the disbelievers,  speak up.   

elsissi
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Re: Modulation marches forward
elsissi   12/21/2013 1:02:21 PM

This article and many similar others in the press in the last week, is an example of what you get when you have a marginally good idea and a lot of money to spend on unsubstantiated PR. There is only ONE patent issued in the company name and several applications (not patents). The patent describe a partial signaling transmitted and a maximum likelihood receiver implementation. It is NOT as claimed in the article which strung together all sorts of unsupported superlatives. What a shame!!

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