Why do that always forget to distinguish between Fixed and Mobile WiMax?
They're two separate standards, with two completely different goals...
I suspect that this apparent divide is where most of WiMAX's woes originate from. In mass market standards (GSM, CDMA etc), there's never really any debate about versions. Equipment vendors ensure that there's always good reason to upgrade to the next version of the standard, particularly to keep up with carefully forecast customer demand, and no-one tries to draw fundamental distinctions between a "d" and an "e". We've gone from 2G to 2.5G to 3G to 3.5G to proposed 4G standards in mobile without any of the great angst that seems to surround WiMAX.
The WiMAX Forum (and the originators of the underlying standards, both the IEEE and ETSI) never really had a coherent vision of what they were trying to develop. Instead, WiMAX has become the future perfect standard for all sorts of things, from the next generation of WiFi, to super-fast fixed broadband to 4G mobile. It's been hyped as delivering 70 Mbps at 70 km/h at a distance of 70 km from the basestation. Of course, in reality, it's none of these. It is the first set of standards to make use of OFDM(A) together with a QoS MAC layer, taking learnings from several generations of WiFi, and some neat basic research into modulation schemes.
As a set of standards, WiMAX is optimum for delivering amongst the highest possible bps/Hz (the real measure of spectral efficiency), and is particularly effective at maintaining this efficiency in a cluttered urban environment. How it ever found its way into being touted as a great wide-area, rural standard is beyond belief. In such environments, it's typically less efficient than the 3G (UMTS/CDMA) standards. Similarly, the whole protocol stack is optimised around carrying packets, typically IP packets. What this means is that it's actually quite inefficient at carrying voice, so it's not much of a challenge to the bulk of the 3G market (which, sadly, is still mostly driven by voice).
As for the distinction between 802.16d "Fixed WiMAX", and 802.16e "Mobile WiMAX", much lies in the (relatively recent) marketing spin adopted by the WiMAX Forum, who are strongly pushing "Mobile WiMAX" as a "4G mobile" standard. In reality, 802.16e has some distinct advantages over 802.16d, most notably its more efficient uplink (OFDMA vs OFDM), its ability to handle cell handover ("mobile"), and the addition of smart antenna techniques to boost performance. Of course, to make a truly mobile standard, there's lots more, including the key parts of the core network that maintain subscriber mobility and roaming. Hence, we have 802.16m, which, I suppose, will be "Truly Mobile WiMAX".
If everyone promoting WiMAX agreed what they were trying to build, we'd have far less confusion over the different flavours, and a proper, backward compatible roadmap (as one finds in GSM, or CDMA standards, for example).
Even a cursory glance at Wikipedia will show you that WiMAX, far from being the perfect 4G technology, is simply an early adopter of OFDMA, which is now being used in the development of real 4G (LTE and its successors). Much will hinge on who is promoting which standard, and I suspect, on balance, that LTE is the likely winner in this race. If this is the case, WiMAX will continue to be more of a niche technology, building a market for itself in developing countries (like South Africa, or India), but never really gaining much of a foothold in developed countries with strong broadband markets, and saturated mobile markets.
