WiMAX Moving Fast Toward Deployment
By Barry Manz, Contributing Editor, MPD

It seems only yesterday that the media and analysts were pondering the question of whether or not WiMAX would actually be deployed. That’s a moot point today. The question today is not if WiMAX will be deployed but how quickly, in how many places, and for what applications. Back in early 2007, when an article in the The Economist sported the headline “WhyMAX?”, it seemed that WiMAX would have to do battle with entrenched wireless networks and the looming Long Term Evolution (LTE) enhancement to UMTS. While that may yet come to be, the pace at which WiMAX is developing means it will expand also into new frontiers, such as rural areas in which there are no competitors that can as quickly or inexpensively “set up shop” to provide fixed and mobile broadband wireless access.

Clearly, WiMAX today is racing faster than any other wireless technology. Networks are either in development or being deployed in countries throughout the world as new infrastructure products reach the market on a monthly basis. Not surprisingly, the U.S. isn’t among the frontrunners in deployment, even though it was conceived here and most of the initial development work was conducted here. The “survival of the fittest” approach to business in the U.S. precludes WiMAX from simply being mandated by some government agency, as has been the case with cellular and PCS networks in Europe and many other countries. However, the potential for U.S. manufacturers to reap the benefits of WiMAX, regardless of where it is deployed, are enormous. In short, WiMAX has tremendous momentum, is strongly backed by some of the world’s largest electronics manufacturers, and is being deftly administrated by the WiMAX Forum and its more than 470 members from all segments of the WiMAX “ecosystem”.

Almost every major wireless carrier is at least considering how WiMAX can fit into its mix of voice, data, and video, and in the case of some carriers, alongside its incumbent high-speed data services. From that perspective, the most vulnerable next-generation data service based on an incumbent technology is the UltraMobile Broadband (UMB) extension to CDMA2000, the future of which is becoming more and more tenuous. When established CDMA2000 carriers such as Sprint Nextel and Verizon Wireless state their commitment to LTE or WiMAX, the future of UMB looks bleak indeed.

However, the potential rivalry between LTE and WiMAX is already showing some signs of being handled more reasonably than simply fighting it out, with the confused consumer as the loser. In fact, to show how LTE and WiMAX may ultimately coexist requires no further study than comments made recently by Sean Maloney, Intel’s head of sales and marketing, who has been at the forefront of WiMAX since the beginning. Maloney said “In our view they ought to be harmonized,” said Maloney. The two technologies were “broadly similar…. about 80%,” he continued, the main difference being that “WiMAX is a couple of years ahead.” Motorola has indicated that 85% of its technology and designs for WiMAX equipment will be reused in its LTE equipment.

Maloney echoed the sentiments of Vodafone chief executive Arun Sarin, who earlier said he felt the two standards could effectively be brought together. Vodafone has its feet in both camps, since it is the “other half” of Verizon Wireless. Vodafone is now conducting WiMAX trials in Greece and Malta and Verizon Wireless is testing LTE.

“We would much prefer to see over a period of time that it looked to a global consumer that simply high-speed bandwidth was available,” said Maloney. “LTE is still a little ways away but as it starts to show up we will be looking to see how we can harmonize with it.” He also said that Intel’s WiFi/WiMAX chipset to be introduced later in the year could also be used for LTE. LTE is not expected to reach mass adoption until 2012 while the first WiMAX networks have already been rolled out.

In terms of other applications, cell site backhaul has always appeared to be a slam dunk for WiMAX, since carriers currently spend enormous sums on T1, fiber, and microwave links to deliver this essential capability. As a replacement for DSL and cable for high-speed residential Internet service, its potential appears likely to be determined market by market. Cable provides high-speed access and its speed is increasing. DSL has become the new dial-up for carriers such as Verizon, which is feverishly deploying its fast FIOS fiber-to-the-home solution to compete with cable. FIOS has been well received where it is available, but it is not widely available yet in most areas and may not be in a wide swath of the U.S. for years. So if cable and (or) FIOS is available, WiMAX will probably be a hard sell, especially since the quality of service provided by the incumbents is generally very good. Nevertheless, in the U.S., that still leaves huge geographic areas in which to tread, and a wealth of opportunities as an alternative wireless broadband service and as the “wide-area hotspot solution” that WiFi has proven it cannot cost effectively be.

The greatest opportunity for WiMAX lies in delivering the same types of services that AT&T and Verizon, the two largest U. S. cellular carriers, are either delivering now or plan to deliver as quickly as possible, largely via LTE. Sprint Nextel, the boldest company to step up to bat for WiMAX, hit a brick wall after it announced an alliance with Clearwire Corp. to deploy a broad-based WiMAX network called XOHM. Changes in management at the company, declining market share for its core services, and shareholder skepticism over WiMAX in general, have delayed – but not killed – XOHM.

If nothing else, Sprint’s headlong leap into WiMAX proved a major lesson for the future: Being “first” may have its promotional benefits, but in practice, “going it alone” is incredibly difficult and expensive. So now a new plan has emerged. Sprint, Google, and some of the largest U.S. cable companies joined forces in May to create the “new” $14.5 billion Clearwire Corp. in the hope of fending off challenges from AT&T and Verizon before they take flight. In addition to Sprint and Google, the partnership includes Time Warner Cable, Intel, and Bright House Networks. Together they plan to build a WiMAX network to deliver wireless access for laptops and other wireless-enabled devices with coverage of 120 to 140 million potential subscribers by 2010 and up to 200 million thereafter. It’s an ambitious plan, but the deep pockets of the players and the ability to combine forces to drive costs down and use Sprint’s extensive infrastructure may be just what’s needed.

Of course, this level of commitment doesn’t come cheap, and Sprint alone will be handing over $7.4 billion to give it a 51% in the venture (XOHM was predicted to cost more than $5 billion). The partners will essentially lease time on the network, while also providing branded Web services. The cable companies can sell Sprint voice and data services as well. As their share of the deal, the partners receive 22% of Clearwire and are expected to contribute $3.2 billion to the project. Clearwire shareholders will get 27% ownership.

Sprint president and CEO Dan Hesse summed up the plan. “For Sprint shareholders, this is an opportunity to unlock and bring visibility to the value of our significant spectrum assets, technology and expertise by leveraging the technology, applications, and distribution strength of our investors, who together command nearly a half-trillion dollars in market capitalization. We’ve made an excellent start developing XOHM WiMAX services. Contributing those advances to a strongly backed new company – in which we’ll hold the largest interest – provides Sprint with additional financial flexibility and allows Sprint management to leverage and focus on our core business.”

Moving Fast
The Clearwire project is a massive undertaking, but its just one of dozens of WiMAX deployments and other activities, news of which appears regularly. The most recent WiMAX Forum Mobile WiMAX PlugFest drew 28 vendors from around the world to demonstrate interoperability and performance of Mobile WiMAX equipment with enhanced testing of beamforming and of Multiple Input Multiple Output (MIMO) technology. It was hosted by AT4 Wireless Laboratories in Malaga, Spain, and WiMAX base stations, mobile subscriber stations, and test equipment manufacturers conducted performance and interoperability testing with other WiMAX vendors at 2.5 GHz. The list of participating members is impressive: Agilent Technologies, Alcatel-Lucent, Anite Telecom, Azimuth Systems, Cisco Systems, Fujitsu Microelectronics, GCT Semiconductor, Huawei Technologies, Japan Radio, Kyocera, Marvell International, Motorola, NEC, NextWave Wireless, picoChip Designs, POSDATA, Rohde & Schwarz, Sanjole, Siemens, SOMA Networks, SR Telecom, Telsima, and Toshiba Corp., among others.

In addition, some of the largest companies in the electronics industry just unveiled a patent alliance that will help promote WiMAX. Alcatel-Lucent, Cisco Systems, Clearwire, Intel, Samsung Electronics, and Sprint Nextel plan to establish the Open Patent Alliance (OPA), which is crafted to foster an open and competitive intellectual property rights model to remove development roadblocks in stimulating WiMAX.

The patent pools will aggregate patent rights to implement the WiMAX standard according to its definition by the WiMAX Forum. A patent alliance has the potential to ensure differentiation and interoperability, while also keeping costs predictable. It will have a competitive royalty structure, charging only for features required to develop new products. An independent third-party reviewer will serve as a referee and evaluate submitted patents to determine their worth using the WiMAX standard and WiMAX Forum profiles. In addition to creating new WiMAX products, OPA will help educate vendors and users about WiMAX and act as a central resource for WiMAX intellectual property rights.

Testing: A Big Challenge
All current digital wireless technologies rely on higher-order modulation schemes, which place significant demands on manufacturers at every level, from active devices through complete systems, and require extensive testing. WiMAX adds to this already formidable task, since it employs not only one higher-order modulation scheme but several, and MIMO, which is essential for optimum WiMAX performance but adds significant complexity (which is increasing as it evolves) and may include beamforming as well.

Fundamentally, characterization of WiMAX products is no different than for any other wireless network, since all are based on fully-documented standards. However, WiMAX is arguably the most complex system ever deployed in commercial service. And while cellular services took decades to reach their current level of maturity, WiMAX begins its life as a high-speed digital all-IP-core network. MIMO requires a historically unprecedented combination of RF and high-speed digital signal processing technologies orchestrated by comprehensive software. Characterizing the performance of a WiMAX system also requires (as do its predecessors) not just basic measurements but interoperability tests to ensure that all user equipment and infrastructure works well together.

MIMO and Its Benefits
MIMO is often loosely applied to cover everything from the use of more than one antenna for transmitting signals, receiving them, or both, along with multiple input and output signals. MIMO exploits the spatial dimension of a radio channel. It can be applied to either the downlink or uplink of a system, the downlink being the base station transmitter, and the mobile (or fixed) terminal being the receiver. The uplink is just the reverse of this. From the perspective of WiMAX user equipment, cost as well as available “real estate” constrains the incorporation of MIMO, so it is more common for base stations to have more antennas than user equipment.

MIMO can significantly improve data transmission performance: diversity gains can increase the quality of data transmission, and spatial multiplexing gains can increase the throughput of data transmission. These two benefits can sometimes conflict, so MIMO algorithms either provide diversity or multiplexing gains but not both. The result is determined by the type of signal processing employed by the system. Diversity gain is accomplished by receiving the same data stream over multiple propagation paths.

Spatial multiplexing gain is accomplished by simultaneously sending different data streams over the same radio resource, which can dramatically increase throughput and bandwidth efficiency. The streams are only discriminated by the spatial dimension -- each stream is sent on a different “layer” of the radio channel together with a specific pilot or reference signal sequence. The receiver can distinguish the data streams sent from the different transmit antennas by their pilot sequence and can perform channel estimation for each stream separately.

Generally speaking, spatial multiplexing gain can only be fully exploited if data streams can be detected and recovered correctly in the receiver, which must solve a linear system of equations (for 2x2 MIMO two equations with two unknowns). This is possible if the channel matrix has full rank, which is achieved if each antenna receives a different channel as is true in strong multipath environments with spatially uncorrelated fading.

Summary
The microwave industry is almost certain to benefit as the WiMAX saga unfolds. Rather than an enhancement to an existing system, which increasing is accomplished via software, WiMAX is an entirely new network, requiring entirely new hardware, from the component level through complete base stations and user equipment ranging from PC cards to handsets and smartphones. Combined with whatever becomes of the 700 MHz spectrum recently auctioned off to AT&T, Verizon Wireless, and other companies, WiMAX represents significant opportunities in the coming years for those with the technical prowess and manufacturing capability to capture them. It will no doubt be a bumpy, fast-faced ride, but one well worth taking.

Barry Manz
www.manzcomm.com
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