There's probably no wireless topic today that's more confusing than WiMax. It doesn't help that there are really two WiMax specifications (one of which doesn't even exist yet), or that the very name WiMax implies a relationship with that other "Wi" that isn't even there.

So, let's start at the beginning. We generally organise wireless technologies by range - the effective distance that the technology, when implemented, is designed to cover. This is the most important parameter in radio design: range determines many key elements of a given product, including physical size, power consumption, cost and the type of antenna required. Less range means smaller, cheaper and (usually) better battery life as well. It also means we can re-use the frequencies involved a short distance away, making the best use of the scarce resource that is the electromagnetic spectrum.

WiMax is for wide areas
We classify WiMax as a wireless metropolitan-area network, or WMAN, meaning it's designed to cover a fairly large area. As I mentioned above, there are two types of WiMax. The first is designed for fixed (as opposed to mobile) applications, as one might find in Internet access installations. This is the current WiMax specification and is based on the IEEE 802.16-2004 standard. This kind of WiMax primarily competes with cable modems and xDSL for residential and business access applications (the WiMax Forum is branding products that meet this standard).

WiMax is thus really a standardisation of one of the oldest branches of wireless - fixed point-to-point and point-to-multipoint (hub or star configuration) topologies. Such systems are particularly useful in emerging economies and in rural areas where wired competition doesn't exist. Properly priced, though, such systems could also compete directly with wired technologies, and lots of wireless ISPs do just that. Since most of the cost of wired networks is in the last mile, I expect this flavor of WiMax to do really well, but competition from proprietary solutions will continue. We're just now seeing the first fixed WiMax products on the market.

Mobile WiMax is tougher
But the version of WiMax that is capturing everyone's attention is mobile WiMax (Intel has promised a mobile card this year). The spec for this technology doesn't yet exist, but it will be based on the very new IEEE 802.16e-2005 standard. The idea here is simple: a metro-scale, broadband, all-IP service with full support for time-bounded traffic like VoIP.

Mobile systems are much tougher to engineer than fixed systems for a number of reasons. First, while we'd like to keep the number of base stations to a minimum because they're expensive, the nature of a given radio connection changes as the mobile end moves. Specifically, fading comes into play, and at times the signal may fade so much that a connection can't be maintained.

We may also have problems with capacity as lots of users attempt to access the relatively limited number of channels available. The solution here is simple in one respect - just add more base stations. Cellular carriers have to deal with this problem on a daily basis, but, again, the expense involved is one of the reasons that cellular systems still feature dropped calls, occasional gaps in service and (often) slow data throughput.

WiMax versus cellular?
In fact, comparisons with cellular are quite appropriate here, since the challenges faced by cellular and mobile WiMax are almost identical. And therein lies the biggest challenge - can mobile WiMax really compete with cellular? Cellular-based wireless broadband services like 1xEV-DO, the version of 3G available in the US from Sprint and Verizon, and HSDPA (High-Speed Downlink Packet Access), available from Cingular, will eventually offer multimegabit data services - exactly the territory mobile WiMax is targeting.

While it's been theorised that the cost of mobile WiMax base stations will be less than that of corresponding cellular equipment, the real costs in operating any wireless network are in spectrum (it's auctioned to the highest bidder), real estate and customer-related functions like marketing, sales and support. WiMax won't have any advantage in these.

WiMax versus Wi-Fi?
Many people have been thinking of WiMax as "Wi-Fi on steroids," and even that WiMax will replace Wi-Fi over time. Both of these suggestions are outside the bounds of reality. Wi-Fi is a wireless LAN and well on its way to ubiquity. Nothing can stop Wi-Fi, and it will challenge WiMax in metro-scale applications.

More importantly, however, Wi-Fi is a "small cell" technology with a range of perhaps a couple of hundred meters under the right circumstances. WiMax is a "big cell" approach, designed to cover kilometers. As it turns out, the combination of big and small is likely the best solution to the coverage and capacity problem. But I don't think the combination of WiMax and Wi-Fi is likely to prevail; cellular is well established in the big-cell space, and WiMax will have a difficult time indeed penetrating that opportunity.

I expect we won't see mobile WiMax until next year, but we'll be following developments in this market closely during 2006.

Mathias is a principal at Farpoint Group, an advisory firm specialising in wireless networking and mobile computing. This article appeared in Computerworld.