Microwave Journal

Making Sense of WiMAX

November 1, 2007

When peering in at the still-evolving world of WiMAX from the outside, it is easy to be confounded by the cloud of information swirling around as the technology works to launch itself into the mainstream. To the layperson, it is possible to conclude that WiMAX has already become hopelessly complex, and it has not even been launched. In an ironic twist, some of the very companies and standards organizations with the most to gain from the success of WiMAX are often, perhaps unwittingly, involved in spreading confusion when they could be fostering clarity. For example, the WiMAX Forum™—the industry consortium that promotes this new, standards-based approach to Broadband Wireless Access (BWA)—talks of Fixed and Mobile standards, while the IEEE has standards with monikers that include 802.16d, 802.16-2004, 802.16e and 802.16-2005; and there are accounts of new releases like 802.16m and 802.16p that further muddy the waters.


The casual observer must ask whether these things are the same or different? Further, the potential for confusion grows when terms like ‘Nomadic WiMAX’ and ‘Portable WiMAX’ are introduced to the global conversation about WiMAX and the technology behind it. Some equipment vendors have even co-opted ‘WiMAX’ to refer to any BWA product, further blurring the line between the standards-based approach championed by the Forum and the pedestrian proprietary products that have been on the market for years. Trying to understand it all is enough to turn even the most seasoned technologist into a closet technophobe. All labeling issues aside, there is a seemingly endless parade of technologically-focused issues that also swirl around WiMAX. Consider all the frequency bands that WiMAX has been purported to use. Then there are the WiMAX Profiles, the WiMAX Releases and the multiple waves of Certification. And even though first-generation WiMAX products are just now taking hold in some regions, there is the irresistible urge on the part of some to speculate about what comes next: the unfortunately named—but inevitable—’WiMAX 2.0.’ Before we all drown in this eddy of profiles and releases and waves, let us try to stem the flow of confusion, separate the wheat from the chaff, and identify what is essential knowledge in tracking this market.

So, let us boldly go where few have gone before in an effort to understand WiMAX, its fixed and mobile variations; how the standards organizations work to bring harmony to the system; and how releases, profiles and certification are designed to foster both interoperability and market growth. It does not have to be as complicated as some might make it seem.

The WiMAX Forum and the IEEE

The first thing to understand about WiMAX is the definition and purpose of the WiMAX Forum,™ and how this differs from the role of the IEEE. The IEEE and the Forum are separate entities. The former defines itself as a “professional association for the advancement of technology,” while the latter is a consortium of companies across the wireless ecosystem (component suppliers, radio vendors, service providers, test equipment manufacturers, software developers, etc.). The Forum brings these players together to help ensure interoperability in a relatively new approach to mobile broadband wireless and helpfully gives us this defining passage on its web site:

“The ultimate goal of the WiMAX Forum is to promote and accelerate the introduction of cost-effective broadband wireless access services into the marketplace. Standards-based, interoperable solutions enable economies of scale that, in turn, drive price and performance levels unachievable by proprietary approaches, making WiMAX Forum Certified™ products the most competitive at delivering broadband services on a wide scale” (www.wimaxforum.org/certification/certification_program).

Like any association or trade group made up of for-profit corporations, it would be naïve to think that all participants in the WiMAX Forum are at the table merely to foster the common good. The Forum’s message is sometimes obscured by individual players’ own tactics as they push proprietary solutions or publicize their own approach; to wit, much of the information about WiMAX in the trades media is clever misdirection generated to point the reader towards ‘ABC Company’s’ better WiMAX mousetrap. That any company invested in WiMAX success would seek to turn the market in a way that favors its own position should not come as a surprise. However, in order for WiMAX to succeed it must be based on common standards, or else this latest attempt at realizing universal BWA will go the way of the turn-of-the-century efforts that were swallowed in the morass of proprietary solution dead-ends. When an approach or equipment solution is championed, the best guidance is ‘caveat emptor’: buyer beware. Is the solution interoperable with those from other vendors? Is it WiMAX Forum Certified (more on that later…)? Is it really WiMAX or just another solution offered for a limited area or market? As indicated in its charter, the Forum’s main goal is to ensure interoperability between all WiMAX equipment. Step one is defining a set of performance standards for a WiMAX radio; step two is the ability and authority to formally certify products that meet those standards. A vendor cannot call its product a “WiMAX” radio unless it is awarded Certification by the Forum—and here we have our first source of confusion. Multiple vendors—including those that are active members of the Forum—have already begun marketing their uncertified products as “WiMAX” radios. The term “WiMAX” has been co-opted by some to refer to any BWA radio, whether it is based on Forum standards or on a proprietary design. If it is a tissue, it’s not necessarily a Kleenex-branded tissue; likewise, just because someone manufactures a broadband radio, it’s not necessarily a WiMAX radio. In fact, it is probably not, since there are only a handful of products that have official Forum Certification to date: http://www.wimaxforum.org/kshowcase/view.

The Alphanumeric WiMAX Soup: 802.16 and Its Many Children

Clearly, the IEEE does the world a great service in its approach to advancement and standardization of technologies. However, in doing so, the alphanumeric soup of standards that it produces tends to confuse the uninitiated when internal working group terms get thrown around. Certainly, the 802.16 standard specifically refers to Wireless Metropolitan Area Networks (WMAN, similar to WLAN—it is the same idea; see Figure 1). But what of 802.16d, 16e, 16f, 16m, 16-2004, 16e-2005? What needs to be known? What can be discarded by the analyst or layperson? Unless membership in an IEEE standards committee or working group is in your future, keep this summary handy. All the standards shown in Table 1 have been referred to by their WiMAX Forum labels (Fixed, Mobile or Release 2.0) for the sake of clarity in the list that follows.

• 802.16d has been terminated. It was the basis for Fixed WiMAX, but it is no longer. Any published reference to it is out of date.

• 802.16-2004 is alive and well, and is the new basis for Fixed WiMAX. To be clear, for all but the most fastidious, ‘Fixed WiMAX’ and ‘802.16-2004’ are different labels for the same thing.

• 802.16e-2005 is the IEEE standard on which Mobile WiMAX is based. It is released and the WiMAX Forum’s Mobile WiMAX Certification efforts will begin at the end of this year. To investigate Mobile WiMAX further, visit http://ieee802.org/16/published.html.

• 802.16m is in the very early stages of definition, but is expected to be the basis for Mobile WiMAX Release 2.0 (Why does there always have to be a two-point-oh? More on that later…). WiMAX Detractors—those that champion other broadband wireless technologies—have seized upon the m in 802.16m and have been telling the market Mobile WiMAX is still in the early committee stages at the IEEE. This is patently untrue; rather, 812.16m is the second generation of Mobile WiMAX.

• 802.16f-2005, 812.16.2-2004, 812.16k-2007… Investigate these further through the IEEE if there is an interest, but there is nothing there that will engender a better understanding of the WiMAX market as it exists today.

Frequency Bands

When looking at any wireless technology, the first set of questions any analyst ought to ask concerns frequency: what frequency band(s) will this new technology use? Is it licensed or unlicensed? Where will this frequency be available? Where will it not be available? The initial simplistic declaration on WiMAX was that it would run at 2.5, 3.5 and 5.8 GHz. The reality is, of course, slightly more intricate than that. While there are still a number of outstanding questions regarding the allocation of licensed frequency for WiMAX, it is generally understood that the United States and Canada will have released licenses in the 2.305 to 2.320, 2.300 to 2.400, 2.345 to 2.360 and 2.469 to 2.690 GHz bands (simplified: this is the 2.5 GHz band). Sprint, incidentally, and its well-publicized $3 B US-wide network, will use the 2.469 to 2.690 GHz band. NextWave Wireless, which owns the lion’s share of the 2.305 to 2.320 GHz (the WCS spectrum) in the United States, has also committed to WiMAX. South Korean provider Korea Telecom™ has already deployed a WiBro system in the 2.3 to 2.4 GHz band and Indian telecom companies have used the 3.4 to 3.8 GHz band (call it 3.5 GHz if that makes it easier) for their early Fixed WiMAX networks in their deliberate but forward-looking deployment strategy. Meanwhile, European Union countries are likely to issue licenses in the 3.3 to 3.4 and 3.4 to 3.8 GHz bands (again, 3.5 GHz). Japan has made available a 4.9 GHz band and, finally, China has not yet formally committed spectrum for WiMAX applications. It should also be noted that while most of the world’s major telecom companies have yet committed to building out with WiMAX, a number of small operators and start-up service providers have begun offering ‘WiMAX-like’ services.

Not mentioned above are the 700 MHz and 5.8 GHz bands, which are unlicensed in most countries. There are two schools of thought for these spectrum blocks. Proponents of the first say, “These bands are unlicensed, so who’s going to want to deploy networks in them? There’s no demand for WiMAX here.” Their opponents say, “These bands are unlicensed, so anyone and everyone can and will deploy networks there. The demand for WiMAX in this spectrum is clearly here.” To date, the WiMAX Forum has not yet released any profiles for these bands, which tells you that the first school of thought has won this argument… so far. Moving forward, Fixed WiMAX will be effectively available worldwide in the 3.5 GHz bands—except for North America, which will use the 2.5 GHz bands. Meanwhile, Mobile WiMAX will likely be at 3.5 GHz in the EU and at 2.5 GHz everywhere else; this will be true if China commits to the plan followed by other key international players instead of charting its own course. In order to get to this level of alignment, the WiMAX Forum has had to address the muddle of frequencies with a two-pronged strategy. First, the Forum works with the world’s governmental regulatory bodies to align available spectrum along a limited set of frequencies, minimizing the need for multiple radio architectures. Second, it provides an environment in which equipment vendors and service providers can work together to determine the bands that the first WiMAX radios will use. This second prong of the attack is manifested in the Profiles discussed later in this article.

Fixed/Mobile/Portable/Nomadic

WiMAX is necessarily split into two basic categories: Fixed and Mobile, the key difference being that the ‘fixed’ services do not support hand-off, while ‘mobile’ services do. Fixed WiMAX, based on the IEEE 802.16d standard, is well defined and WiMAX Forum-certified radios have been deployed in various markets across the globe. There is a lot of chatter in the industry about “portable” or “nomadic”—or even “luggable”—devices. This is more of a mental exercise in hair-splitting than a division based on legitimate operational differences. For all but the most exacting mind, these two superfluous categories can be lumped into the ‘fixed’ camp. Perhaps a better word for Fixed WiMAX is ‘Fixed-Nomadic WiMAX,’ as the protocol covers both truly-fixed scenarios like “wireless DSL” as well as laptop-based “extended WLAN” nomadic settings in which a subscriber using the network shuts down his/her laptop, moves to another area with service, and then restarts and reconnects. In any case, Fixed WiMAX has a head start: it has already been deployed. Mobile WiMAX is based on IEEE 802.16e-2005 and, just as in the cellular world, allows a subscriber to move from one coverage area or ‘cell’ to another through a series of seamless hand-offs. To date, the only build-out of Mobile WiMAX is in Seoul, where Korea Telecom has launched its WiBro-branded service. There has been agreement within the Forum to meld WiBro and Mobile WiMAX into a single standard, eliminating the confusion of two names describing essentially the same service. Do not expect WiBro to die, though—KT has created a valuable and identifiable brand, and one would expect that Korean WiMAX networks will continue to carry the moniker.

Profiles

It should be noted that WiBro devices have not yet been approved for interoperability by the WiMAX Forum. A good reason for this is that the Forum has not yet released any of its mobile profiles for certification. That said, the March Mobile WiMAX Plugfest (a closed-door event held by the Forum to bring together competing equipment vendors with the goal of testing interoperability) in Southern France included nearly 100 unique successful connections of base stations and mobile stations from approximately 25 different equipment vendors. These vendors worked with six different certification profiles in three frequency bands. At the time of this writing, the October Plugfest in Taiwan was forecast to improve on these numbers. The lesson is that positive progress has been made—and continues to be made—in the development of interoperable devices from varying vendors. All well and good, but what is a profile?

Profiles may be one of the most commonly misunderstood topics surrounding Forum activities. As mentioned before, certification remains at the core of the Forum’s ‘cause d’être’ because of the basic premise that interoperability accomplishes little if the consumer doesn’t have confidence that his new WiMAX PCM/CIA card will work on the new WiMAX network in his neighborhood. Certification equals confidence to the average end user. Given the importance of a formal certification, the Forum is releasing profiles for certification: sets of requirements that must be passed by a given vendor’s base station or subscriber station in order to get Certification: the Forum’s stamp of approval. The multiple RF bands in which WiMAX may be deployed were covered earlier. In order to define a profile, the Forum identifies an RF band, then couples this with a specific channel size as well as a particular duplex mode. For example, one Fixed WiMAX profile for which certified equipment is available is 3.5/3.5/TDD: the 3.5 GHz band, a 3.5 MHz channel, Time Division Duplex mode; the other duplexing mode available for Fixed WiMAX is FDD: Frequency Division Duplexing. Tables 2 and 3 illustrate the profiles that have been formally defined by the Forum to date. The text in the mobile WiMAX table refers to the name assigned by the Forum to a particular profile. All profiles for mobile WiMAX are TDD.

Releases and Waves

There is a natural conflict between implementing innovative new ideas (which often takes longer than initially estimated) and getting products to market quickly. In order to balance this conflict, the Forum has decided to introduce its certification profiles incrementally, allowing for improvements in functionality and features over time. This incremental or ‘staged’ approach is manifested in the Forum’s introduction of Profiles in Releases and Waves. Very simply, Releases and Waves define a set of functionality, with a ‘Wave’ being a subset of a ‘Release.’ The first iteration of WiMAX is Release 1.0—fairly straightforward, really, while Release 2.0 (called WiMAX 2.0 by some wags) is still being developed by the IEEE. Remember 802.16m? This will eventually become Release 2.0—but for the time being, Release 1.0 is all the market really has. Waves are subsets of Releases. The first set of Mobile WiMAX products (certified under Release 1.0, Wave 1) includes support for real-time applications, full mobility, high throughput, and well-defined security and power save mechanisms. Release 1.0, Wave 2 will include advanced features, such as Multiple Input Multiple Output (MIMO) radios, Beamforming, and Multicast Broadcast Services. It should be noted that all subsequent Releases and Waves will be fully backwards compatible. In addition, they will be incremental in nature. For example, Forum certification for Wave 2 will include all the same tests as Wave 1, plus new ones.

Power Amplifier Requirements—Flexibility

Power amplifier technology will be a key to the proliferation of WiMAX. Early WiMAX-based handsets, for example, have proved problematic for widespread usage because of deficient battery life and the fact they tended to heat up during extended use—critical shortcomings. In addition, these devices could stand to have more powerful transmission signals: longer transmission distances from the device will allow for fewer base stations, reduced cost of network build-out, and a quicker ROI for service providers. Heat, battery life and transmission power are all controlled—to a major extent—by the efficiency and linearity of the PA in the user device. An efficient PA uses less power and emits less heat; a PA with high linear output power will necessarily transmit further.

The beauty of the WiMAX Forum mission is that it brings together the parties designing networks, those designing radios, and those creating components to ensure that the right parts are being developed for overall market success. But for all this togetherness, there are still a wide variety of requirements—sometimes conflicting requirements—for the PA and other components. In some regards, the power amplifier has become one of those ‘make-or-break’ components in the system. In a very real way, a good PA is necessary for the success of the whole WiMAX market because without it, more base stations will be required to support large-scale WiMAX deployments. Battery life drains more quickly in mobile devices if the PA efficiency is, in effect, ‘deficient’ and heat build-up becomes a headache for the mobile subscriber. Any negatives along this chain spell trouble for new products in a new market. To the list of PA ‘must-haves’, that includes good output power, efficiency and linearity, one has to also consider the various band requirements (2.305 to 2.320, 2.300 to 2.400, 2.345 to 2.360, 2.469 to 2.690, 3.3 to 3.4 and 3.4 to 3.8 (while this doesn’t even take into account the unlicensed bands at 700 MHz, 4.9 GHz and 5.8 GHz.). Plainly stated, current generation PAs cannot meet these requirements. In addition, WiMAX products also have to fit into various form factor requirements. For example: a fixed WiMAX CPE for a desk at home or in the workplace (think of it as a wireless DSL modem) will need to have different efficiency and bias voltage requirements than a device performing the same function in a mobile PDA or handset. A PA needs to meet this whole suite of requirements while at the same time being cost-effective. The upshot is that a PA must be flexible enough to deliver power in multiple bands, meet varying efficiency versus linearity versus power output requirements, and function in differing bias conditions in different form factors. And it must do all of this at a price that allows the WiMAX market to thrive.

The WiMAX Future

While coming to grips with the ins and outs of WiMAX takes some determination, it would all be for naught if the service doesn’t meet global demand for universal broadband wireless access. What that demand is, incidentally, has been described as a desire to take today’s Internet experience on the road. Nortel calls it “Hyperconnectivity;” NextWave calls it “WiMAX 2.0;” and the well publicized Xohm (pronounced “zome”) service from Sprint calls it “Personal Broadband.” In every case the concept is remarkably straightforward: providing connectivity to any online application, anywhere, at any time, on any device. At the Mobile Broadband Executive Summit this preceding September’s WiMAX World show, Sprint’s Atish Gude pointed out that those looking for the so-called killer application that will drive the market are missing the devastatingly simple point that “Access is the killer application.” Underscoring this point at the same event, the Yankee Group’s Phil Marshall shared survey data indicating that approximately 40 percent of consumers would like a wireless broadband service, but only a quarter of these people actually subscribe to any of today’s options. Overwhelmingly, the reason for this gap is a price/speed tradeoff—nearly 70 percent of the remaining three-quarters believe that current options are too expensive and/or do not realize the broadband data rates required to replicate the wired Internet experience. With the assumption that the standardization efforts of the Forum will bring prices down and engender widespread network deployment, TriQuint Semiconductor’s own product marketing group projects strong growth through 2012 based on its understanding of the forces shaping demand and the availability of Certified equipment (see Figures 2 and 3).

But just as wading through the swirl of information around WiMAX takes time, so does any analysis of the market forces that will affect uptake by the consuming public. As has been demonstrated before, even technically sound ideas supported by well-financed development and market roll-outs do not always reap immediate success. But for market watchers, there is general agreement that the overall worldwide economic outlook favors continued expansion of wireless communications, with wireless broadband access being the main component of that growth. While no one can say what the full impact of LTE, ‘super 3G’ or other flavors of 4G technology will be, as cellular vies to meet the demand for broadband service, it is clear at the same time that WiMAX offers advantages that make it a strong contender for a healthy portion of the BWA market. WiMAX offers advantages across what has been called the 4 Cs: Cost (favorable cost structure through mass standardization); Capacity (higher order modulation schemes, wider channel bandwidth); Coverage (Orthogonal Frequency Division Multiplexing provides superior non-line-of-sight-performance); and Convergence (the 802.16 family and WiBro/Mobile WiMAX enable rapid evolution of globally standardized technology). It is most likely that the future of broadband access will include a number of vehicles for service delivery involving both the ‘legacy’ worldwide cellular network as well as both fixed and mobile WiMAX solutions. As has been seen with almost anything involving data storage, data rates and the public’s demand for communications services, ‘good’ always demands ‘better’, and ‘slow’ is intractably replaced by ‘faster.’ With demand for data rates continually growing, and since the nature of global communications is becoming increasingly mobile, wireless broadband access will continue to be a growth market into the second decade of the 21st century.

Josh Raha is a product marketing manager focusing on the WiMAX, Bluetooth and GPS markets for TriQuint Semiconductor in Orlando, FL. Before joining TriQuint, he was in product management for Triton Network Systems. He holds a BS degree in electrical engineering from the University of Pennsylvania and an MBA degree from the University of Southern California.

Mark Andrews is marketing communications manager for TriQuint Semiconductor in Orlando, FL. He has authored numerous papers and articles focusing on the needs of technology-focused communications industries since 1993. He has a BS degree in fine and applied arts from Central Michigan University.