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« Students in Rochester Build Metro Network | Main | Yet Another Spectrum Auction »

August 8, 2006

Fundamentally, WiMax Is Meant for Licensed Bands

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.


I think there is too much demand for unlicensed WiMax for this profile not to develope. Even if it is never sanctioned by the WiMax forum, vendors will come out with something that is functionally equivalent and based on the same ASICs (to keep the price down). If you question the demand, just look at the campus (corporate, hospital, school, whatever) market. This is a market where you have a strong desire for a non-contention MAC (see Meru Networks and other solutions) but still a desire to have complete control over the installed equipment and not have to rely on what a spectrum license holder is willing to provide you. I think unlicensed WiMax, in fact if not in name, is a foregone conclusion.

[Editor's note: All good points, and I don't dispute them. What I wonder if whether a non-certified unlicensed profile winds up being uniformly adopted by enough copies to allow cheap CPEs that support that profile.--gf]

There is no advantage real advantage for unlicensed WiMax. The FCC part 15 limitations and having to deal with contention overwhelm anything that WiMax might do. And as you point out, WiFi has been evolving in that environment for over a decade now.

But i would not portray WiMax as the 21st Century tech. The tech in WiMax is no newer than WiFi. And I would say that WiFi, due to having to compete, is evolving at orders of magnitude greater than WiMax.

There will only be a small number of customers for WiMax in the US. They will all be carriers. They will all have carrier mentalities. Those two conditions will guarantee that WiMax will not evolve fast nor will it be cheap.

WiFi, as it recapitulates the evolution of Ethernet, will out evolve and be dramatically cheaper than WiMax. Leaving WiMax to a few small niches and expensive carrier plays. (IMHO)

[Editor's note: Have to disagree with you on the newness of the tech. The Wi-Fi MAC is very old, and creaky. OFDM is pasted on. It can't support TDD or FDD for scheduling. OFDMA is much cooler. QoS was pasted on. Certain security models were pasted on. Many heterogeneous devices dating to 1999 are in use. And so on.--gf]

I find your blog both on the money and accurate to the fullest and, while I too like the potentiality of WiMAX, I think WiFi could use some of the WiMAX QoS features even if they are mostly theoretical at this point. I realize that we can accomplish QoS through different layers and devices at this time, but I would really like to see an emphasis on it as you do in WiMAX.

Interestingly, one could make an argument that QoS is more sorely needed in the high contention world of WiFi than the licensed world of WiMAX. I suppose only time will tell.

Thanks again for a great thought provoking blog.

Tom Carpenter
Author - Wireless# Certification Official Study Guide

What about AMD? You think they are going to sit back and let Intel "own" WiMax? I know they've said they are not going to pursue the centrino-like strategy, but whats to stop them from changing their mind a few years down the road?

I think it's important to have availability in unlicensed bands for certain public entities. For example, if a police department or a school district wants a fixed or mobile link set up across campuses or an entire city, unlicensed WiMAX could work. I suppose there is no good reason that is has to be standard WiMAX rather than a proprietary technology like Moto Canopy or Proxim Tsunami, but the WiMAX name at least makes people more aware of its availability.

From a service provider perspective, you are right on about licensed WiMAX being the best way to go.

[Editor's note: Good points, and note that some institutions have assigned wireless licenses! Many of them then leased those licenses to Sprint Nextel and Clearwire in exchange for what was once a small amount of money and now is apparently quite large. That would be not quite ironic, but slightly funny.--gf]

OFDM, MIMO, Security were "pasted" on to WiFi just as 100Mbps, 1Gbps, 10Gbps, fiber, jumbo frames, etc were "pasted on" to Ethernet and Ethernet blew by "pure, more modern" standards like AnyLan VG and ATM.

WiFi is the Ethernet and WiMax is the ATM of wireless.

Just like ATM had some success in carriers, WiMax will have some success in carriers. But it will never get the scope and depth of deployment that WiFi does and will have. And WiFi wil out evolve WiMax because WiFi the fabric of the fast, deep, wide and cheap standard.

And I agree with you about Unlicensed WiMax but that is one of the key reasons why WiFi will out-evolve WiMax. The cost free and "jungle like" environment allows / requires WiFi to evolve fast and deep. But WiMax in the captive-garden of carriers just breads weakness.

I think the answer to your question has already been provided by 802.11n. Still no WiFi Forum certification for this profile, but I can buy some fairly cheap consumer grade equipment already. Given how influential Cisco is in the campus environments I mentioned, if they supported 802.16 that would be as good as a WiMax Forum profile. The flip side of this is Centrino. If Centrino comes with support for 802.16 in unlicensed bands bands, even if not sanctioned by the WiMax Forum, isn't that enough of a market for infrastructure vendors to go after? Final thought: what's in it for the WiMax Forum to not support some unlicensed profiles? If anything, they stand to make more money by doing so -- more profiles means more ceritifcation fees.

[Editor's note: 802.11n doesn't answer any of the issues that I raise with WiMax versus Wi-Fi. And the Wi-Fi Alliance won't certify until the standard is set, which is now probably fall 2007 given today's word that Task Group N (which decides on 802.11n's standard) won't have a new draft for ballotting until January.

The WiMax Forum doesn't operate on money; it operates on the will of member companies that decide what profiles make sense for marketing and technical deployment.--gf]