Your quick WiMAX technology primer, including speeds, notebook adaptors, base stations, VOIP gear, and whether it will blow away 3G.
It’s touted as the future of wireless broadband, and more significantly for Australian users, the technology that may help to bridge the gap between rural and urban broadband speeds. It’s WiMAX (Worldwide Interoperability for Microwave Access), a wireless data transmission technology with a whole lot of potential application – and more than a few pitfalls.
Wireless on Steroids
At its most basic, WiMAX uses an existing high speed broadband technology at one end – this can be anything from ADSL up to high-speed fibre – connected to a transmitting tower.
Those who love acronyms will be in seventh heaven with WiMAX’s technical specifications. The fixed variant uses Orthogonal Frequency Division Multiplexing (OFDM), while the mobile version uses Orthogonal Frequency-Division Multiple Access (OFDMA). So what the heck’s OFDM/A? At a basic level, it splits all of the modulated data signals being sent into discrete packets that don’t overlap and allow for a lot of data interference – as would be the case over such long distances. The OFDMA is, if you will, OFDM on steroids; the mobile version requires far more redundancy (and the ability to quickly recreate packets) to avoid signal fading, as you might get indoors or on the edges of acceptable signal ranges.
Interference Issues
WiMAX installations can either be done on the public airwaves (unlicensed spectrum), or across a heavily regulated spectrum (licensed spectrum). It’s possible that WiMAX technology may become cheap enough that players do emerge in the unlicensed spectrum, but the possibilities for interference are exceptionally high; for the moment licensed spectrum is the way to go, and that limits the number of players depending on who holds the licences for that particular spectrum. Although the specification is consistently evolving, at the time of writing, the spectrum in question is in the 2.4Ghz and 3.4-3.5Ghz bands.
WiMAX speed and range
The top rated speed of a single WiMAX tower is currently stated at 70Mbps. Before you start drooling and/or throwing out your WiFi and ADSL gear, there are limitations within that. Firstly, without installation of some relatively complex household antennae equipment, WiMAX doesn’t work well without direct line of sight between towers – similar to the way that mobile phone signals drop out in tunnels or buildings without the use of repeaters. Secondly, there’s the distance equation. The top range of a fixed WiMAX tower is typically around 50 kilometres, almost exactly ten times that of a current wired ADSL signal. Mobile WiMAX installations typically quote around 15km with a line of sight, but much less in heavy urban areas, where you may only get 1-2km of coverage.
Further complicating matters is the fact that you can’t transmit 70MBps over anything like 50km; as the distance increases, the speed drops. The number of WiMAX users for a particular tower further affects available bandwidth. That 70MBps of throughput has to be shared amongst all users, and it’s pretty much up to the ISP as to how many subscribers they assign to a given tower.
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