April 30, 2010, 8:08 PM — While you're waiting for WiMAX or other 4G data technologies to roll out, you might be interested in knowing that a new, faster still, WiMAX2, is on its way.
WiMAX (Worldwide Interoperability for Microwave Access) is slowly making its way into businesses and homes. With its promise of average speeds of 4 to 6Mbps (Megabits per second) and coverage areas of square miles instead of square yards, WiMAX has long promised to be the next generation of Wireless networking. Now, faced with competition from LTE (Long-Term Evolution), WiMAX supporters are upping the ante with WiMAX2.
According to the WiMAX Forum, the industry trade group that supports WiMAX, the new WiMAX will be more than 50 percent faster than today's WiMAX while remaining compliant with the existing IEEE 802.16e standard. WiMAX 2 is built on the still evolving IEEE 802.16m standard. If it works the way its designers want it to, WiMAX2 equipment will be backward compatible with existing WiMAX hardware while delivering double the peak data rates while increasing the average and cell edge end user performance by 50 percent.
So, how are they going to pull this trick off? Here's the techie details.
How WiMAX Works
Like most high-speed wireless technologies, WiMAX achieves high data rates in part via OFDM (orthogonal frequency division multiplexing). OFDM increases bandwidth by splitting broad channels into multiple narrowband channels -- each using a different frequency -- that can then carry different parts of a message simultaneously.
To be exact, both WiMAX and WiMAX2 uses scalable ODFM, which increases bandwidth by not only splitting a data-bearing radio signal into smaller signal sets; but by modulating each onto different sub-carriers, spaced orthogonally to minimize interference; and assigning subsets of sub-carriers to individual base stations.
Each of these channels, in turn, uses a technology called QAM (Quadrature Amplitude Modulation) to pack more data into each channel. In the case of WiMAX2, the standard mandates the use of 64 QAM. This means that each signal can be in one of 64 different phases.
Like 802.11n, the new, fast Wi-Fi technology, both WiMAX and WiMAX2 uses another technology called MIMO (Multiple input, Multiple Output). MIMO uses multiple antennas as transmitters and receivers to reduce errors and improve data rates by better capturing the signals that scatter during a typical transmission.
MIMO isn't just about adding antennas though. No, what really makes MIMO work is that MIMO takes advantage of multipath interference. What's that you ask? This kind of interference shows when transmitted signals reflect off objects and take multiple paths to their destination. If you’ve listened to a radio station’s signal wax and wane as you move by large buildings in a city, you’ve heard multipath interference in action.
With commonplace antennas, like those on your car, the signals arrive out of phase and interfere with one another. MIMO systems take those out of phase signals and uses them. It does this by employing multiple antennas to use these reflected signals as additional simultaneous transmission and reception channels. Once the signals have been received, MIMO knits the disparate signals together to produce a single, faster network connection. What the new standard brings to this is that it will include support for additional MIMO antennae on the base stations -- four transmit antennae instead of two.
In addition, WiMAX2 will include downlink beamforming. What this means is that as your laptop, smartphone or what have you starts working with a base station, the system will work out what your SINR (signal-to-interference noise ratio) levels is and use that information to work out the best way to transmit data to you based on the existing radio conditions. Of course, if you're moving in say a car while using a WiMAX2 connection, you won't get the advantage, but WiMAX2 supporters reason that you're more likely to be reading ITworld or watching a Netflix video from your office or a coffee shop rather than a bus.
