If OFDMA is the new standard, the road to today’s WiMax has been an unusual one in other ways. The core wireless technology, embodied in the first version of the IEEE 802.16 standard, harks back to the tail end of the dot-com heyday. It was designed for an immobile device that would sit in a home much like a DSL modem—except without needing an expensive wire or cable connecting it to the outside world. By 2004, wireless equipment makers were producing antennas and end-user devices that could exchange data at DSL-like speeds.
At the same time, though, one researcher, Hui Liu, now an associate professor at the University of Washington in Seattle, was solving the basic problems of mobile communications between OFDMA-based transceivers, such as handoffs from one cell tower to another. First at one company, Cwill Technologies in Austin, Texas, and then at another, Navini Networks in Richardson, Texas, a leading maker of WiMax equipment, Liu applied his work to the then-new fixed 802.16 standard. In early 2005, the South Korean government pushed the country’s leading telecommunications companies, such as Samsung, to commercialize mobile WiMax within 18 months.
What the Experts Say
”Vertically integrated service providers will lose market share to horizontal businesses with open application environments and universal device access. Sprint’s WiMax deployment will help break the users’ bondage to traditional carriers.”
Researchers elsewhere were skeptical, but by 2006, WiBro (as this South Korean version of WiMax was called) antennas were going up in Seoul and other cities. The version of the 802.16 standard that Xohm adheres to is a little different—it uses 10-megahertz channels, for example, while WiBro’s are 8.75 MHz, and a number of additions have been made, including several that fall under the rubric of ”quality of service”—but Korean eagerness to combine mobility and broadband speed can be credited with its breakneck development and much of the lead today’s WiMax has over LTE.
Although both LTE and WiMax use OFDMA, there are some differences of course, and according to Doug Smith, Sprint’s chief technical operations officer, the net result is that WiMax will be more spectrally efficient, packing more data transmission into the same bandwidth. For one thing, LTE uses a frequency-division scheme: it divides its assigned spectrum into two different channels, one for transmission and the other for reception, with a guard band between them to prevent interference. WiMax uses a single channel and divides it by time—sending, then receiving, then sending again. Frequency division is simpler, but the guard band wastes a small but precious amount of spectrum. In addition, the relative sizes of the two channels are fixed, while in a time-division scheme more time can be allocated as needed for sending or receiving.
Smith says that initially, the network will allocate about one-third of its bandwidth to uploading, that is, to letting users transmit files. That’s far more than other wireless—or wired—services do. ”If people are doing more downloading, then we can give even more time to it. We’ll have to see how the network is used. A video blogger might upload more than download,” he notes.
No one can say today just what LTE data rates will be, but we do know that WiMax does a lot better than HSPA. For a given 10 MHz, HSPA has a maximum throughput of 7.2 Mb/s downloading and 2.2 Mb/s uploading. WiMax, by contrast, gets up to 37 and 6 Mb/s, respectively.
In addition, Sprint has more of those 10-MHz segments than its competitors. It started to acquire spectrum in the 2.5â¿¿GHz band back in the heady dotâ¿¿com days of the late 1990s. Coincidentally, Nextel did as well, a key reason Sprint regarded it as an attractive takeover target. It has also been swapping snippets of spectrum with Clearwire in each other’s cities. All told, Xohm will have 120 MHz of spectrum in most of its markets. By comparison, AT&T and Verizon each only have about 50 MHz for their 3G networks today (which use the 1.9-GHz band).
Ideally, carriers like to divide each cell into three sectors, using directional antennas that limit themselves to 120 degrees of coverage. Such a scheme is called a reuse of 3. By using a different frequency in an adjacent cell, interference at the edges, where the cells meet, is minimized.
Ali Tabassi, Sprint’s vice president of technology, says that ”in order to truly deliver mobile wireless broadband, one needs to have 10 MHz each for the downlink and the uplink, with a reuse of 3.” A time-division transmission scheme like HSPA would need 60 MHz of spectrum to do that. That’s a little more than what AT&T and Verizon have, but it’s only half of Sprint’s holdings.
In the long run, LTE will have much higher data rates than HSPA. And because LTE is designed to be an easy upgrade from GSM and HSPA, it will let carriers get those higher data rates in their existing 1.9-GHz spectrum. Most GSM operators will move to LTE, so it’s also likely to have a broad base of suppliers, carriers, and users—an ecosystem—from the outset. On the other hand, Xohm, Clearwire, and other WiMax-based networks will have a three-year head start in the marketplace.
Building a new network from scratch is a gargantuan task—one that, fortunately, Sprint doesn’t have to undertake. For one thing, between its CDMA and other networks, the company starts with over 50 000 cell sites. Over the next year and a half, it will add WiMax radios and antennas to about 12 000 of them and create about 3000 new cell sites.
Smith insists that Xohm will be the fastest-built network in cellular history, and it just might be. Sometime this month Chicago and the Baltimore–Washington, D.C., area will get the service on a precommercial basis—a beta test of sorts. Full commercial service in those metropolitan areas is slated for this coming April. Other locales will quickly be brought online, culminating with New York City late this year. In broad terms, Sprint is working on tier 1 cities—the largest ones—while Clearwire concentrates on tier 2, places like Portland, Ore., and Grand Rapids, Mich.
Whether Xohm thrives will depend on more than just the number of people it’s available to. Equally important are the services it can conjure up—including the mysterious, as-yet-undefined ones that Hanson spoke of. Of course, would-be providers of these services will want to see the millions of users first.
And it’s actually a lot more complicated than that. The service providers—for example, online game companies that want to build mobile versions of their games—won’t take the plunge unless they see a panoply of devices—laptop cards, smart phones, ultramobile PCs, and so on—with which users can access the network. Yet hardware manufacturers are usually reluctant to design and build those devices unless there is a big, obvious market of customers—the same customers Sprint needs to attract in the first place.
Sprint plans to break into these vicious circles within circles by assembling its own WiMax ecosystem. It has chosen three big manufacturers—Motorola, Nokia, and Samsung—to make handsets and laptop cards, as well as the radios and antennas that will go on rooftops and towers, and the routers and servers that will connect them to the Internet as a whole. Sprint has gone to extraordinary lengths to ensure that the three vendors—and a fourth, Intel—will be able to test their equipment and its compatibility with that of other companies, including cellphone makers ZyXel of Anaheim, Calif., and ZTE in Shenzhen, China. Each of the four has its own area, which it can keep under lock and key, within Xohm’s own testing lab at its Herndon, Va., headquarters.
Perhaps the best thing that Sprint has going for it is that Xohm is merely a focal point for a growing interest in WiMax. In October, for example, Cisco Systems, of San Jose, Calif., the router giant, bought Navini Networks. In all, the WiMax Forum claims about 500 members. In addition to Cisco, some key ones outside the immediate Sprint orbit are Fujitsu, General Dynamics, Nortel Networks, Siemens, and Alcatel-Lucent, which was shut out of Xohm but built the system for the Dominican Republic that was turned on in October. Alcatel-Lucent has contracts to build WiMax networks in Europe, Brazil, China, and elsewhere. Meanwhile, phones using Google’s gPhone design may show up in the second half of the year.
As for the ecosystem of service providers, Xohm has several things going for it. First, as it is an open Internet platform, thousands of existing applications and services—Google search, instant messaging, iTunes, peer-to-peer music file sharing, you name it—will work just as they do with any other broadband connection. And according to Hwan Woo Chung, a vice president in Samsung’s telecommunication systems division, the network will not only be open enough but also fast enough to allow Internet-based television and other video transmissions to flow without noticeable latency.
Sprint will probably offer voice calling on the network, but users can bring their own Internet-telephony programs—Vonage, Skype, and the others—to Xohm. These programs will work as they do on landline broadband—generally pretty well, occasionally less so. The quality-of-service provisions in the WiMax protocol let a carrier protect certain types of transmissions, giving their data packets a higher priority as they travel through the network. Sprint would of course protect its own voice packets. Doing so raises, again, the question of network neutrality, because Vonage’s unprotected voice-over-IP service, for example, won’t work as well as Sprint’s own.
Sprint’s Hanson knows this is an issue. ”We’re not in the business of picking winners and losers,” she says firmly. ”We’re an open network. The more data transmitted across it, the more money we make, in the long run.” And indeed, a company like Vonage, of Holmdel, N.J., could pay Sprint to protect its packets equally. If Sprint is willing to do that for any voice-over-IP provider, and similarly treats other applications and application providers, then the network will, in practical terms, be neutral.
Net neutrality will become a bigger issue only as the Internet continues to mature and as the major carriers and service providers get larger in size and fewer in number. Two months ago, AT&T announced it would use a software program to inspect the YouTube videos that its subscribers try to watch, blocking any that might infringe the copyrights of the major record labels and movie and television studios. It’s just one example of how your Internet experience will differ depending on the company from which you access it—an early fracture, critics say, in the unity of the Net. Against that, a new Internet provider promising an open network—and a fully mobile, wireless one at that—will be a welcome addition.
Xohm—A Fully Mobile Broadband Network
Goal: To blanket the United States with high-speed Internet access, even in a moving train or car.
Why It’s a Winner: It combines the two fastest-growing areas in telecommunications: cellular and high-speed Internet access.
Player: Sprint Nextel
Where: Reston, Va.
Staff: Info not available
Budget: US $3 billion