beam-forming

What’s New in Wi-Fi: 802.11AC

Sometimes it’s worth it to stay until the bitter end. In this case, for a “What is Wi-Fi?” workshop, which ended at 5:30 on a Friday afternoon in a week that contained two back-to-back conventions – first CTAM Summit, then the SCTE Cable-Tec Expo.

Wi-Fi matters to cable providers for two reasons: One, as a way to make existing broadband customers more “sticky” by offering easy access to signal when on the go – doctor’s office, sporting event, train station. Two, for the potential revenues associated with helping other carriers (think mobile operators) to offload the huge volumes of data clogging their pipes.

This week’s translation attempts to condense that hour-and-a-half workshop, led by Jerry Patton, product manager / wireless network for Arris, and Daniel Howard, CTO of the SCTE. Here goes.

So: What’s new in Wi-Fi? “802.11 ac,” the latest shoptalk darling of Wi-Fi. In its sexier marketing finery, 802.11 ac goes by “Gigabit Wi-Fi.” So, theoretically, that means 1,000 Megabits per second. (What!) Compared to the fastest advertised broadband speed – 300 Mbps – that’s pretty zippy.

But hold on. Before going any further with Wi-Fi speeds, know that almost every number you hear is smaller or slower than it really is. There’s a physical rate, and then there’s an actual rate.

The physical rate is the “if all things are perfect” speed. In wireless (especially outdoors), things are never perfect.  Wireless access points are constantly besieged with noise. Impulse noise, ingress noise, spurious noise.

Actual throughput rates are typically 30-40% slower than what an access point may be capable of (physical rate), in perfect conditions. The rest is the overhead of re-sending whatever it is that got squelched by noise.

Here’s what to know about 802.11 ac: It works (only) in the 5 GHz band, which means that any “clients” (phones, tablets, laptops) equipped 2.4 GHz radios won’t work. (So far, only the Apple iPhone5 is plumbed with 802.11ac, but it’s early yet.)

Gigabit Wi-Fi gets to those willy-nilly speeds using a feature familiar to cable modem operations: Channel bonding, of up to 8 channels. In reality, it’s unlikely that eight clean, contiguous channels exist. Plus, recall that speed is a function of modulation, which almost always includes a tradeoff between speed and sturdiness.

So, watch for 802.11ac as more of an in-the-house thing (and when you replace your Wi-Fi router, make sure that it’s IPv6) than an outdoors thing.

Bonus round Wi-Fi shop talk: “Beam-forming.” It’s a way to bulge a Wi-Fi signal out toward the devices it serves, rather than shooting out signal omni-directionally.  The work of it can happen on chip, or in an antenna; best to ask. Also good to ask: How many streams it takes. Because every stream that’s beam-formed can’t be used for anything else.

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