Things tend to occur in threes. Add broadband access methods to the list, with WiMAX—the wireless broadband metropolitan networking technology—now bursting onto the scene. Competing with cable and DSL, WiMAX (Wireless interoperability for Microwave Access) passed through its early development and standardssetting phases and is emerging from the product design stage into the real world of applications.
Some pre-WiMAX and WiMAX-like systems are out there now, but look for real products later this year and early in 2006. Expectations run high, as is the case for any new and promising technology. But it remains to be seen whether this superior wireless system will be adopted by the mainstream or end up as a niche for select wireless needs.
Initially, WiMAX was developed as a broadband access technology for metro-area networks (MANs). The IEEE standardized it as 802.16-2004 (802.16d), primarily for fixed (not mobile) point-to-multipoint (PMP) and point-to-point (P2P) services between homes and/or businesses and a nearby basestation, such as a cell site.
The frequency of operation between 2 and 11 GHz depends on geography. The most common bands are 2.3 to 2.5 GHz and 5.8 GHz in the U.S. and 3.5 GHz in Europe and Asia. Both licensed and unlicensed spectra are available.
Maximum data rate is 75 Mbits/s. A majority of systems will allocate that in lower-rate segments, depending on bandwidth and application. Channel bandwidth can be set from 1.75 to 20 MHz. The standard uses time-division duplexing (TDD) or frequency-division duplexing (FDD), whichever best fits the application.
FDD provides full duplex, but it's most often found in licensed spectra where paired frequencies are available. TDD is used for unlicensed applications. An adaptive modulation scheme adjusts the modulation method, which relies on the distance from the basestation, noise, multipath, and other typical wireless conditions. It also includes binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) for longer-range connections and 16QAM or 64QAM for shorter ranges.
The basic access mode is 256-point orthogonal frequency-division multiplexing (OFDM). Using OFDM will mitigate the multipath problems and solve the line-of-sight (LOS) problem associated with earlier microwave access problems. In addition, consumers can use either an indoor antenna or a simple outdoor antenna that doesn't require precise orientation.
Maximum transmission range is about 30 miles, but typical basestation radii will be more like 2 to 10 km. Full power control at both the basestation and the customer premises equipment (CPE) is implemented to optimize the signal for each subscriber. The system is compatible with the newer sectorized, adaptive, and beamforming antennas.
In a fixed service, a single basestation is expected to handle a few dozen T1/E1-like connections for businesses and several hundred consumer connections that have rates comparable to existing DSL and cable lines. Though Internet access is the most likely application, WiMAX also can handle Voice over Internet Protocol (VoIP) and video.
Last-mile/first-mile service is expected to be WiMAX's main application, but whether it can compete head-on with the well-entrenched existing cable and DSL service is still unknown. Of course, it will be a boon to customers in urban areas beyond the reach of a DSL line or without cable service. Rural areas that lack both services also will benefit.
Another major application involves inexpensive backhaul for cell sites and Wi-Fi hot spots. Both of these typicallyuse expensive T1 lines. In addition to eliminating cables, the equipment and service will be much less expensive and easier to install and provision. Since that T1 connection is the biggest cost of an 802.11 access point, look for WiMAX to greatly expand the number of hot spots around the country.
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