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October 2009 | Volume 12 / Number 10
Next Wave Redux

Wireless Broadband Alternatives (Hint: It’s not WiMAX or LTE)

Think about broadband wireless Internet access, and WiMAX (News - Alert) comes to mind. Kudos to the WiMAX Forum. But whether it’s WiMAX or mobile’s long-term evolution, cellular point-to-multipoint wireless standards won’t win in the end. They are critical for mobile phone service for at least the next decade, and they will be critical for mobile data access over a similar period. But fixed and nomadic Internet access will play out somewhat differently because new technology is changing the rules.

Of course fiber performance beats that of wireless over comparable distances. But fiber installation is relatively expensive, especially to low-density rural areas, and it requires rights-of-way that in most cases are locked up by monopolists. These monopolists are regulated under legacy legal frameworks completely unrelated to the Internet. Wireless is the only alternative, so it’s worth understanding how new technology is changing traditional wireless rules.

Until recently, lower frequencies were more valuable, since signals on them traveled farther. But this was due to technology limits, not physics. Atmospheric absorption is the same for signals from 50 MHz (below TV channel 2) to 10 GHz (way above TV, cellular and WiFi (News - Alert)). Higher frequencies have shorter wavelengths and, in the past, this was a disadvantage. First, low-cost antennas scaled by wavelength so shorter wavelengths meant smaller antennas, which gathered less energy. Second, short wavelengths are more easily reflected and refracted from everyday objects like buildings, window sills and file cabinets. The result is multiple, slightly offset versions of the original signal (so-called “multipath” interference), which confused radio receivers.


But as silicon devices become more powerful, we can afford to decode multiple signals, adjust signal offsets and sum them. What was a disadvantage becomes an advantage in new multiple-input, multiple-output (MIMO) radios, already deployed for “802.11n” WiFi and soon to be deployed with WiMAX and LTE (News - Alert). Since there is vastly more spectrum available at 5 GHz than the sum of TV “white spaces” plus licensed WiMAX and cellular spectrum, WiFi capacity will vastly exceed that of WiMAX and LTE.

Next up is beamforming – electronically steerable high-gain antennas. Early WiFi products are just coming to market, but the next two to three years of silicon performance improvements will result in highly directional WiFi signals with much greater range. Directional signals dramatically reduce interference, allowing multiple independent high-capacity transmissions in the same area. The ability to support multiple long-range connections makes it dramatically easier to build mesh networks.

Exactly how it all plays out is not clear yet but, with affordable WiFi routers supporting multiple connections of 200 to 500 Mbps each over distances of one to two kilometers, there will be many interesting alternatives. IT

Brough Turner is chief strategy officer of Dialogic (News - Alert) (www.dialogic.com).

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