It seems like it takes forever for any new wireless technology to work its
way from initial idea through standards adoption to useful products. After the
long development cycles of 3G cell phones, Bluetooth, Zig-Bee, Ultra-Wideband
(UWB), and Wi-Fi (including 802.11n), you have to wonder if something is wrong
with the system.
When you dig below the veneer of hype, though, you can see that WiMAX is moving forward just fine. It isn't a perfect technology, but it fills the metropolitan-area network (MAN) niche. And if the technology continues at a steady pace toward adoption, it should find its place alongside the many complementary wireless and non-wireless systems already in place.
WiMAX REDUX
Short for Worldwide Interoperability for Microwave Access,
WiMAX refers to a MAN that promises high-speed data access over a major geographic
sector. WiMAX is similar to Wi-Fi, but the key difference is that WiMAX has
a maximum range of a few miles instead of Wi-Fi's few hundred feet.
WiMAX is based upon the IEEE's 802.16 MAN standard. Earlier versions targeted the 10- to 66-GHz bands with a line of sight (LOS) system capable of data rates of 34 to 134 Mbits/s using quadrature phase-shift keying (QPSK), 16QAM (quadrature amplitude modulation), or 64QAM at a range up to about 3 miles. More recent versions started with 802.16a, which defined an orthogonal frequency-division multiplexing (OFDM) physical layer (PHY) with 256 or 2048 subcarriers and a single carrier version.
This was subsequently revised and updated in September 2004 for the 2- to 11-GHz range with a non-line of sight (NLOS) objective, the so-called 802.16-2004 standard for fixed wireless service. The 802.16e-2005 standard for mobile service, which was ratified in December 2005, uses orthogonal frequency-division multiple access (OFDMA) and can potentially achieve a mobile data rate of 15 Mbits/s max at a range to 3 miles.
The primary WiMAX application is high-speed Internet access. It would compete head on with entrenched broadband systems from cable TV and DSL suppliers, but the chances are good that the technology will win out in the end. You'll hear the expression broadband wireless access (BWA) applied to WiMAX and any similar broadband wireless system.
WiMAX also promises to be an alternative 3G mobile Internet access service. It makes a good low-cost backhaul technology for cell-phone basestations or Wi-Fi access points as well, meaning that it should be a lower-cost wireless T1 line replacement.
The fixed version of WiMAX has been around for a few years, but with limited adoption—at least in the U.S. More WiMAX silicon and equipment is sold in other parts of the world, but that's expected to change. Developing countries, as well as those with huge swaths of area in need of high-speed Internet coverage, are picking up on the technology.
That's because WiMAX is a faster, lower-cost method for offering broadband
connections, rather than stringing or burying cable. More and more, telephone
systems using Voice over Internet Protocol (VoIP) over WiMAX are being installed
over more conventional wired local service. India is just one of many countries
where WiMAX is beginning to supply not only high-speed Internet access, but
also phone service.
In the U.S., the hope is that WiMAX will provide broadband services to rural areas and small towns that are underserved by cable TV and DSL providers. And it's even happening in some areas. Bell South is currently testing services in rural Mississippi, Tennessee, Louisiana, Georgia, and Florida.
WiMAX is designed for service in the 2- to 6-GHz microwave range, where licensed or unlicensed spectrum is available. The outer limit of its capability is a 75-Mbit/s data rate at a range to 30 miles. But it's doubtful anyone will use it in that form. Instead, WiMAX will be deployed by building a network of basestations with coverage radii in the 2- to 6-mile range. All that speed will be divided up among many users, with most getting a solid data rate in the 1-to 3-Mbit/s range. Businesses can pay for more speed as needed.
WiMAX uses 256 OFDM and adaptive modulation (binary PSK, QPSK, 16QAM, and 64QAM—depending
upon range, noise, multipath, etc.) as well as a wide mix of bandwidths (1.25
to 20 MHz) and data rates under differing conditions.