Beyond WiMAX: Gigabit Wireless

000126aWiMAX, with its promise of super-speed wireless Internet access, is nearly here. Defined as “a standards-based technology enabling the delivery of last-mile wireless broadband access as an alternative to cable and DSL,” WiMAX is capable of data speeds around 100 megabits per second, and can send that signal over several miles — though speed drops off as the range increases.

Yet research is already underway into WiMAX’s successor. Some of the most promising results so far use millimeter-wave technology, as such systems should be able to deliver data over the air not at megabits-per-second rates, but rather at many gigabits per second. That’s approaching the speeds you can get over fiber-optic connections.

Like other 802.xx IEEE wireless data systems, WiMAX uses centimeter-range radio waves to carry digital data. In the U.S., the frequencies allocated to WiMAX mean it will operate around 3GHz, giving a carrier wavelength of 10cm. This is convenient for antenna design, and practical data rates over WiMAX are in the tens-of-megabit range. ISPs are planning to use the system to complete the “last-mile” connection between their service and consumers’ homes, since it brings massive infrastructure advantages alongside speed boosts.

In contrast, millimeter-wave technology operates at radio frequencies of between 60 and 100 GHz, giving the waves lengths of 3-5mm. It’s a part of the radio spectrum commonly used for radio astronomy and high-resolution radar systems, and it’s largely unregulated and unused — particularly compared to the crowded, longer wavelength end of the spectrum.

It’s interesting for data communications for one main reason: Millimeter-wave transmissions, since they use a higher frequency than other wireless standards, fit more data into their signals at a higher rate. This is simply due to bandwidth. A higher bandwidth signal can carry more data, and chopping up MHz radio-frequencies creates signal bands with a particular width. Doing the same with GHz radio frequencies creates similar bands with a greater width, essentially creating a fatter radio “tube” through which data can be sent.

Despite obvious advantages, the difficulties of building technology that can encode signals onto millimeter-sized carrier waves means millimeter-wave communications have gone largely unused.

But that’s changing. A Columbus, Ohio-based company called Battelle has recently demonstrated a 20-gigabit-per-second data transmission system in its laboratory. It’s based on off-the-shelf technology that encodes data onto optical telecoms laser signals; when two of these lasers interfere, the resulting optical interference pattern acts a 100-gigahertz signal, in the millimeter-wave spectrum. Another company, Gigabeam, already has products available that can do point-to-point 1Gbps communications using millimeter-wave transmitters and receivers.

Millimeter-wave communications have other advantages. Antennas can be smaller than those used for longer wavelength radio waves, which is great for portable gadgets. And the signals can be more precisely directed, which even allows for a greater density of signals to occupy the same physical space without interfering.

Ultimately, why do we care about millimeter-wave wireless? Due to our thirst for more data at higher speeds. The wireless communications infrastructure we’ve been building will someday hit its inevitable maximum capacity, and data rate throttling by some ISPs shows they’re already trying to protect their wired broadband data distribution networks from being overloaded. Fiber optics can offer bigger data rates and higher capacity, but obviously don’t work for mobile solutions — something we’re also increasingly demanding as consumers.

It’s a question of numbers. The complete works of Shakespeare (around 5 MB of text) can be transmitted over typical existing Wi-Fi in seconds, while a gigabit millimeter-wave wireless network could do the same in a few tens of milliseconds. Given our need for speed, the future choice of consumers seems pretty clear.

Image of low-cost, millimeter-wave front-end module courtesy of NEC.

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