Data

How to Talk to People Who Use the Word “Orthogonal”

by Leslie Ellis // September 04 2012

Here’s one that’s sauntering back into tech-speak: Orthogonal.

Orthogonal is an oldie-but-goodie tech term, sure to imbue the person who utters it with an unmistakable whiff of tech intelligence. (It has nothing to do with your feet or shoes.)

As an everyday term, though, “orthogonal” is still largely inscrutable: A (math) term, meaning “at right angles.” Generally speaking, when people say “orthogonal” and they’re not talking about OFDM (yes there are people who say “orthogonal” conversationally), they mostly mean “irrelevant.” One thing doesn’t affect or disaffect the other thing.

In cable tech-talk, listen for “orthogonal” in tech-talk from broadband-side technologists working on what comes next with the DOCSIS cable modem specification. One of the potential expansions: OFDM, or, Orthogonal Frequency Division Multiplexing.

Know going in that OFDM is an upstream modulation thing, just as is QAM (quadrature amplitude modulation), QPSK (quaterny phase shift key), and S-CDMA (synchronous code division multiple access.)

Refresher: Modulation is the process of imprinting information onto a communications carrier, itself an electro-magnetic wave, so as to move that information from one physical location to another.

So, people talk about OFDM in the context of getting more stuff upstream, or responding to faster upstream speeds. (OFDM could be used for downstream modulation, too, but that’s not the initial application.)

OFDM, with improved error correction, could kick up some serious capacity – half as much again as what’s already down there. Which is good, because the upstream path is a slender five percent of total available capacity on any cable system.

How to earn style points when talking to engineers about OFDM: Ask the person who utters “OFDM” what they think Hedy Lamarr would say, if asked how it compares to her invention of CDMA. (A variation of which – Synchronous CDMA, or S-CDMA — is still used in cable modems.)

Lamarr, a celebrated MGM actress in the ‘30s and ‘40s, was romantically involved with a ranking military official in Europe, and endured the tedium of being treated as a bubblehead long enough to collect the facts she needed to develop what is now CDMA. (It also goes by “spread spectrum.”)

CDMA works by compartmentalizing a signal into a series of packets, which are smeared across a chunk of spectrum for transmission. It was initially used by the Dept. of Defense to transmit coded information. It’s like OFDM in that it codes data to move over smaller spectral slices.

But in every other sense, OFDM is essentially orthogonal to your everyday life.

This column originally appeared in the Platforms section of Multichannel News.

Move over, Moore — Shannon’s Law Is On

A few weeks ago, an engineering elder called to pose this bit of industrial wisdom: “For the last 20 years, we’ve seen the monetization of Moore’s Law. From here on out, we’ll see the monetization of Shannon’s Law.”

Haven’t heard of Shannon? Welcome to this week’s translation.

First off, one important distinction: There are laws, and then there are “laws.” Think laws of gravity, motion, thermodynamics, and physics here. Not legal law, or laws of unintended consequences, or marketing lingo that sounds peppier with “law” in the title.

In that sense, Moore’s Law isn’t technically a law; Shannon’s Law is a law of physics. It’s a physical law, meaning it’s true, universal, simple, absolute, and stable.

Moore’s Law is more of an economic observation, eponymized by Gordon Moore, co-founder of Intel Corp., who wrote a paper in 1965 stating that the number of transistors (processing power) within chips was doubling about every 18 months. It’s still true.

By contrast, and more relevant every “connected” day, is Shannon’s Law. It’s named for Claude Shannon, who did his work 20 years before Moore, in the 1940s.

Shannon’s Law defines “the theoretical maximum rate at which error-free digits can be transmitted over a bandwidth-limited channel in the presence of noise.” (It comes with an equation but we’ll spare you the math.)

In other words, Shannon figured out a way to calculate how much stuff can be crammed over a broadband network, without problems, even when there is noise, which there always is.

The dramatic rise in broadband usage – upwards of 50% compound annual growth – is true on fixed and mobile networks. In London last week, some social media outlets got bogged down because of all the gadgetry trying to send Olympics pictures and videos. We are gunking up networks.

Which is why it’s important to be able to calculate throughput maximums on data networks. And to be able to ease the situation – by adding spectrum, or mitigating noise.

In cable tech circles, invoking Shannon usually means you’re having a conversation about upstream (home to headend) signaling. It’s why there’s so much talk about advanced modulation, and finding ways to make that slender spectral area carry more stuff.

Will Shannon’s Law get monetized like Moore’s Law did, with a fury of investment and development that lasted a half century? Let’s hope so, for the sake of clear connections and unclogged networks.

This column originally appeared in the Platforms section of Multichannel News.