Slashdot Mirror

← Back to Stories (view on slashdot.org)

Cringley On Bandwidth-Expanding Modulation Technology

Posted by ryuzaki0 on from the ten-times-the-fun dept.

jtappan writes: "Robert X Cringely has an article describing a new modulation technology that will allegedly allow cable modems to run 10 times as fast, and which will eventually allow existing cable networks to carry 500 HDTV channels."

5 of 332 comments (clear)

  1. Sounds like what happened with modems by redelm · · Score: 5, Informative
    Well, at least they're not claiming they can beat Shannon's limit. 10 Gbit/s doesn't sound too unreasonable for coax. If you can't drive the frequency higher than say 500 MHz, you could still encode a constellation of 20 bits per transition.


    This is similar to what modems do. AFAIK, they still don't run any faster than 3750 baud (Hz),
    but they can encode up to 15 bits per wave to get 56kbit/sec. If the line isn't so quiet, they cannot distinguish all 15 bits, so the modems have to negotiate a constellation with fewer bits.


    My question is how this will work with an ethernet-like collison detection system that AFAIK cable modems use. The jam signals could get ugly, and I'm not sure you can carry as my info on broadband as baseband systems. Or how cable decoders will cope.

  2. Cringley and the OSI model by aderusha · · Score: 5, Informative

    while i enjoy cringley columns, his mangling of the bottom layers of the OSI model made me cringe (pun intended).

    encoding systems are physical (layer 1) technologies, not 2nd layer like he claims. he further states that ethernet and token ring are layer 3 technologies, which is blatently false - they are both data link technologies.

    maybe i'm just being nitpicky....

  3. Cablemodems can already be much faster than we get by technopinion · · Score: 4, Informative

    I'd rather see advances in backbone speed than last mile speed, thank you. Cable modems are already capped at a fraction of their potential because of insufficient capacity at the ISP side. Give the ISP a couple of gigabit connections, open up the cablemodems to 10mbits, and I'll be perfectly happy, for a couple of months anyway...

  4. Re:Can anyone explain wavelets? by the+eric+conspiracy · · Score: 5, Informative

    Wavelets are an alternative to Fourier Transformation of time domain data to obtain a functional decomposition of the waveform for analyis or processing. They are particularly useful with choppy or spikey signals.

    It's a very fundamental mathematical tool for any kind of signal processing application. As such it has a wide range of applications. It came into wide use perhaps 15 years ago; perhaps you were out of school by then. I am sure that every EE undergraduate is getting exposure to wavelets these days.

    Here is a link to resources on Wavelets:

    http://www.mathsoft.com/wavelets.html

  5. Re:Great! by isdnip · · Score: 5, Informative

    Mr. Z is correct -- moderators, promote the note I'm replying to! Cringely is wrong about layers. Layer 1 does all the bit stuff, including modulation and even ATM cells. (Layer 2 is about user-sized frames and error detection.)

    But that's not what matters. Shannon matters. You can't defeat Shannon, and Cringely admits it. So let's see... Shannon basically says that the limit of bps is proportionate to the product of bandwidth times the log2 of the signal to noise ratio. So if you have an infinite SNR, you can have infinite bandwidth. But getting 33 Mbps (around the top end of DOCSIS cable modems) requires good SNR. My cable modem right now has 36 dB SNR and is running QAM64; DOCSIS adapts speed to line quality.

    So even if wavelets were better than QAM (and I can't say, because Cringely doesn't tell enough to know if this is real or a scam), there's just not that much more you can do in 36 dB! (Shannon limit of 6 MHz at 36 dB is around 6M*12=72 Mbps.)