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y_sasaki
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CEO
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 :-)

Bert22306
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CEO
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.

sridhar.ramesh
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Rookie
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.

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.

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.

paragdighe
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Rookie
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

rick merritt
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Author
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.

rick merritt
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Author
Re: Modulation marches forward
rick merritt   12/18/2013 10:54:26 PM
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@y_sasaki: Nice job runing the numbers.

Does this mean 11ac is about at the limits of what can be done with WiFi and the new modulation scheme won't help? If so, what does that imply for our march to faster, faster, faster?

y_sasaki
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CEO
Re: Modulation marches forward
y_sasaki   12/18/2013 12:55:26 PM
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Correct me if I made mistake.

 

Frii's equasion is C=Blog2(1+S/N), while C=data rate (bit/sec), B is bandwidth (Hz), S/N is simple signal-noise ratio (not in dB).

While is is easy to define B, but assuming S/N is trickey part. Typical WiFi usecase is signal level around -70dBm, while background noise floor will be around -90dBm, so SNR is about 20dB.

 

Based on 802.11ac standard, 256QAM MCS9 datarate is 200Mbps per stream with 40MHz channel, short GI, coding rate 5/6. Raw (pre-FEC) rate is 240Mbps.

240=40*log2(1+S/N)

log2(1+S/N)=240/40=6

1+S/N=2^6=64

S/N=64-1=63

S/N(dB)=10*log10(63)=17.99

 

So it proves 802.11ac MCS9 is within typical usecase, even though 2dB margin is pretty low. Of course "typical" usecase could be varied - you'll get -50 - -60dBm signal if your PC is close to AP (within 10ft) so MCS9 will be much more practical.

 

Theoritically, 4096QAM (64x64 constallation) is 16bit/symbol so it should have x2 datarate than 256QAM (16x16 constallaton, 8bit/symbol). Thus, we can assume 802.11ac 4096QAM must have x2 datarate than 256QAM MCS9.

480=40*log2(1+S/N)

log2(1+S/N)=480/40=12

1+S/N=2^12=4096

S/N=4096-1=4095

S/N(dB)=10*log10(4095)=36.12

 

It shows "4096QAM WiFi" will be inpractical (so I don't think WiFi will adopt more-than 256QAM modulation / stream). Even if their claim of +10dB advantage is correct, 26dB SNR will be still tough to find in public wireless networ (WiFi or LTE).

However, it will make sense to backhaul, where dedicated frequency band is used with much higher TX power and highly tuned directional antenna.

dt_hayden
User Rank
CEO
Issued Patents
dt_hayden   12/18/2013 12:05:55 PM
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A list of 15 issued patents is here.
1 8,605,832 Full-Text Joint sequence estimation of symbol and phase with high tolerance of nonlinearity
2 8,599,914 Full-Text Feed forward equalization for highly-spectrally-efficient communications
3 8,582,637 Full-Text Low-complexity, highly-spectrally-efficient communications
4 8,572,458 Full-Text Forward error correction with parity check encoding for use in low complexity highly-spectrally efficient communications
5 8,571,146 Full-Text Method and system for corrupt symbol handling for providing high reliability sequences
6 8,571,131 Full-Text Dynamic filter adjustment for highly-spectrally-efficient communications
7 8,566,687 Full-Text Method and system for forward error correction decoding with parity check for use in low complexity highly-spectrally efficient communications
8 8,565,363 Full-Text Fine phase estimation for highly spectrally efficient communications
9 8,559,498 Full-Text Decision feedback equalizer utilizing symbol error rate biased adaptation function for highly spectrally efficient communications
10 8,559,496 Full-Text Signal reception using non-linearity-compensated, partial response feedback
11 8,559,494 Full-Text Timing synchronization for reception of highly-spectrally-efficient communications
12 8,553,821 Full-Text Adaptive non-linear model for highly-spectrally-efficient communications
13 8,548,097 Full-Text Coarse phase estimation for highly-spectrally-efficient communications
14 8,548,072 Full-Text Timing pilot generation for highly-spectrally-efficient communications
15 8,526,523 Full-Text Highly-spectrally-efficient receiver

 

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=0&f=S&l=50&TERM1=magnacom&FIELD1=ASNM&co1=AND&TERM2=&FIELD2=&d=PTXT

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