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« The Night the Lights Went Out in Wi-Fi | Main | News for 6/10/2002 »

June 9, 2002

Illuminating RF Lighting

Yesterday's entry about the Robert X. Cringely column discussing the interference issue with Wi-Fi was apparently too obscure for many people. I understand that: it was written as a reaction to an article that explained some of the issues involved, but my response required a lot of knowledge of the area.

Here's a shorter, more comprehensible version of the same article. The executive summary: Other uses of the 2.4 gigahertz (GHz) band that's the home of Wi-Fi may result in such widespread interference that Wi-Fi networks won't be possible indoors or outdoors in many urban areas. That's the long and short of it.

The longer version is that Wi-Fi (or 802.11b or AirPort) doesn't live in its spectrum neighborhood by itself. As I've written in the last few weeks, there are not only licensed neighbors as varied as TV stations' video uplinks, law enforcement, and amateur radio operators -- each of which requires specific permission to use these frequencies -- but also other unlicensed uses which can produce signals that muddle Wi-Fi's transmission.

Unlicensed uses include what the FCC calls Part 15 devices, which includes Wi-Fi, 802.11a, Bluetooth, HomeRF, and cordless phones, as well as Part 18 devices which are used for scientific, industrial, or medical uses. The equipment maker must get FCC approval for specific devices and combinations of equipment -- like an access point with a specific antenna attached -- but the end users and purchasers can use the equipment without requiring any involvement with the FCC whatsoever.

Unlicensed Part 15 equipment is follows a spec that allows it to work over short distances and produce limited interference so that many similar devices can work within relatively small areas without interrupting the utility of any other. If you have two or more uses that overlap and interfere, you can get the FCC to intervene, or try to work it out yourself.

Part 18 equipment has a different set of specifications, but because Part 18 devices typically don't carry data (not in any example I've seen, at least), they don't have the non-interferring requirement, either.

Steve Stroh, the writer, editor, and publisher of Focus on Broadband Wireless Internet Access last summer identified a strong candidate for causing interference: RF (radio frequency) lighting. RF lighting uses radio waves to illuminate lamps. It's apparently very efficient in a number of ways and could radically reduce the cost of exterior lighting.

Read Stroh's article for the full scoop; I won't simply reiterate his points here. He raised this alarm last summer, and Cringely's column is, in part, about how no one else appears to be aware of or is alarmed by this coming problem.

Because RF lighting is an industrial use, it will spew frequency all over the place. While Wi-Fi is good at sorting out signal from noise, there's a potential that RF lighting will sufficiently obscure data to render Wi-Fi networks, especially outdoor hot spot networks useless.

As Stroh and Cringely noted, and I expanded on in my article yesterday, there's a simple solution already well underway. The FCC opened the 5 GHz band (nearly 300 MHz of spectrum in three chunks) for unlicensed Part 15 devices. There are practically no users in this space, and the 802.11a (soon to be known as Wi-Fi5) protocol is designed for 5 GHz.

802.11a has some limits in terms of distance and penetration, so that different system designs will be needed to use 802.11a in areas that currently use Wi-Fi. But it's an uncluttered space that has the potential for greater density of overlapping networks. 802.11a runs at 54 Mbps (raw) compared with Wi-Fi's 11 Mbps, and 22 Mbps with Wi-Fi's 2.4 GHz successor, 802.11g.

Also, as a deployment issue, Wi-Fi has just three channels that can be used at the same time in the same space without causing interference; 802.11a has 12, eight of which are supported by the first-generation equipment.

This fall, we will see many devices that can handle both Wi-Fi and 802.11a, which will aid a transition, especially in corporations to using 802.11a equipment instead of Wi-Fi.

With the millions of Wi-Fi devices already installed, and millions more being sold this year, it's a hard egg to suck when we all tell you that Wi-Fi won't be the technology of the future. But it's increasingly likely that Wi-Fi's place will be remanded to interior applications far from industrial users (your next-door neighbor probably doesn't have a microwave-based plastic sealer) and RF lighting installations.

Etherlinx Couples Radios

John Markoff describes a quiet, inexpensive startup, Etherlinx, that plans to change the face of the final mile: New York Times reporter Markoff details how two innovators a few doors down from Apple's historic garage are taking off-the-shelf Wi-Fi cards, installing their own firmware, and producing CPE (customer premises equipment) devices for less than $100. The dual-radio design allows them to run a long-distance high-bandwidth connection relayed to a local Wi-Fi network. What's unique about this product is that it's a single device and it's cheap. You can assemble equipment like this for $500 to $1000 using telco-grade systems, or you can cobble it together for much less, but still a few hundred dollars and a fair amount of configuration and some supporting devices. More information as it appears.

Wireless Overview

Comprehensive overview of the state of wireless networking:'s newest reporter, Brian Morrissey, presents a superb and comprehensive overview of what's what in Wi-Fi or other 802.11 specs today.