I keep seeing phrases like "WiMax is Wi-Fi on steroids." It's not. Here's why: The fundamental difference between WiMax and Wi-Fi is that WiMax is intended for licensed spectrum in which contention among providers with different interests is eliminated; Wi-Fi is designed for a hostile environment in which every party must accept interference within the legal limits without complaint.
WiMax works over long distances because the spectrum band rules in which it will be deployed for licensed service allow higher signal strength and have higher parameters in every area than the FCC Part 15 rules (and similar regulations internationally) that define Wi-Fi's use in 2.4 GHz and 5 GHz band. WiMax also benefits from the licenseholder coordinating among itself. Wi-Fi lives and dies by contention, a fear in municipal-scale networks.
Wi-Fi is a best efforts technology. Like an eager and precocious child in a raucous classroom full of other precocious children and noisy underachievers, Wi-Fi struggles to be heard while not stepping outside the rules. It often is heard, but its answers to some question are drowned out or need to be repeated. Sometimes, it takes a lot of effort to just spell serendipity because it has to say each letter loudly and slowly for the teacher--the access point--to hear what it's saying.
WiMax is a service level agreement (SLA) technology. WiMax is a private symposium with a talking stick in an elite, organized, and expensive university. In each classroom in the groves of academe, you find extremely well-turned-out students in bespoke clothing, none of whom dares speak without tacit permission of the profession. In fact, it's a bit more like watching staged readings of synchronized poetry than it is a discussion. There is no contention, and each professor rules each classroom as a captain rules his or her ship.
Before you get huffy out there and say, hey, there's going to be unlicensed WiMax, too, or, there's already unlicensed WiMax, think again. There is no unlicensed profile yet approved for WiMax. Any device that uses 5.8 GHz may be lovely, full of light and truth and the joy in exciting electrons into different states at high frequencies, but it isn't certified WiMax. Further, the word is that there may never be a certified profile for the unlicensed bands.
The 5 GHz band gets a real workout, especially 5.8 GHz with its special point-to-point rules for higher signal gain, in metro-scale Wi-Fi networks because it's the only affordable way to backhaul data, and by using highly directional signals, they can bypass quite a bit of the interference issues in that band. At least for now.
Now, I have been pigeonholed as pro-Wi-Fi because I run this blog with the title Wi-Fi in it. I also run a WiMax blog and have for years (originally with help from a colleague). My allegiance is to the consumer rather than the technology, and to the application rather than the physical medium over which applications run. I am not afraid to say that Wi-Fi is often the best-worst technology for a given situation. I could also say that Wi-Fi technology is fundamentally a mid-90s approach to wireless networking wrapped in modern encodings for speed. (Even 802.11n suffers from this.) WiMax is a 21st century technology that has roots in the past, but fewer of the past's limitations.
With more WiMax in the mix in the US, as now is inevitable (whether it's financially advantageous to the firms involve), we will see a lot more tradeoffs between Wi-Fi and WiMax. Wi-Fi's key advantages today are that it works, it's deployed, it's cheap, and it's in practically every laptop. Fixed and mobile WiMax will have some of those advantages within one year.