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These days the standard garnering the lion's share of attention in the communications industry is the Worldwide Interoperability for Microwave Access (WiMAX) specification (IEEE 802.16). WiMAX provides a high-throughput broad-band connection at speeds of up to 75 Mbps over a distance as far as 30 miles. On average a WiMAX base-station installation will likely coverthree to five miles. The technology can be used for a variety of applications including a “last mile” broadband connection, hotspot and cellular backhaul, and high-speed enterprise connectivity for businesses. While some believe that WiMAX is destined to become as widely used as digital subscriber line (DSL) and cable modem Internet access technologies, others feel that its true potential lies in its mobility. Existing cellular operators could use WiMAX networks to supplement their net-works in metropolitan areas, while new operators might deploy the technology to compete with the cellular networks.

Of course, cellular operators aren't sitting idly by waiting for that to happen. Instead, they are looking to the flurry of emerging 3G standards like CDMA2000 1xEV-DO and EV-DV (data and voice) or the WCDMA high-speed download packet access (HSDPA) and highspeed uplink packet access (HSUPA) overlays to give them the range, throughput and flexibility they need to remain competitive and keep consumers happy (Table 1). WiMAX proponents claim that in the long run, it will be cheaper and faster to deploy than cellular. Using the licensed 2.5 GHz band, for example, they expect the upfront costs of mobile WiMAX to be less for the same coverage. And, since these same proponents plan to deliver WiFi speeds with cellular range, at 700 MHz WiMAX might cover the same range with one-third the number of towers.

While 3G cellular technologies stand ready to forge new territory in terms of performance, many in the industry are counting on the fact that WiMAX will deliver on its vision of mobility. The question that remains to be answered is if WiMAX's ability to deliver this broadband wireless performance, on a mobile basis, will really turn the market in its favor. Or, will the market remain faithful to existing modem and cellular technologies, if for no other reason than that they work just good enough to get the job done?

The mobile version of the WiMAX standard, 802.16e, would allow WiMAX technology to be built into notebooks and other mobile devices so that people could communicate while walking or riding in cars. This specification is an extension of 802.16-2004 — the fixed version of WiMAX — that provides transmission to stationary devices using the 2 GHz to 11 GHz frequencies. Higher frequencies require line of sight. 802.16-2004 enables the creation of high-speed, fixed wireless broadband networks, which provide Internet connectivity, Internet protocol (IP) and TDM voice capabilities and IP-based real-time video at high speeds.

The 802.16e specification is expected to be ratified before the end of 2005 and will quickly be followed by product samples, certification, and volume rollout. Helping in that regard will be the WiMAX Forum (www.wimaxforum.org); an industry-led organization formed in 2001 to promote and facilitate the deployment of broadband wireless networks, based on the IEEE 802.16 standard, by certifying compatibility and interoperability of broadband wireless products. Certification will take place via the WiMAX Forum certified testing and certification program. As of July, the organization officially began testing products for WiMAX Forum certification at the Cetecom Labs in Spain.

With certification now under way, chipset makers have focused their attention squarely on the 802.16e specification and the question of which modulation scheme it should employ. While orthogonal frequency-division multiplexing (OFDM) was chosen as the modulation scheme for 802.16 fixed applications, the modulation scheme for 802.16e is still up for debate. The frontrunner, scalable OFDM access (OFDMA), is being touted by companies like Intel (www.intel.com) who feel it can handle the fourfold increase in complexity over fixed WiMAX, different power and coverage requirements, and higher link budgets that are all specific to 802.16e.

In contrast, Wavesat (www.wavesat.com) feels that OFDM 256 Fast Fourier Transform (FFT) will provide the much needed backward compatibility to 802.16. By serving as the physical layer in both fixed and mobile WiMAX systems, future base stations should be able to recognize and operate both fixed and mobile applications; assuming, of course, that the physical layer has, at minimum, the same number of carriers (256) and FFTs.

The choice of a modulation scheme for 802.16e is a crucial decision because it will surely impact the operators' desire to implement WiMAX. Choosing a scheme that provides them the assurance of backward compatibility to fixed WiMAX solutions, while also allowing them to preserve their initial 802.16 investment, will be key.

Despite the questions of modulation schemes and uncertainty about the direction of mobile WiMAX, progress on the fixed WiMAX front is continuing at a steady pace. In order for any technology specification to be successful these days it requires, at minimum, three basic components: an officially standardized specification, an industry organization to promote the standard and vendors to build equipment compliant to the standard. Today, the 802.16-2004 fixed WiMAX specification has each of these components covered.

The last component came earlier this year when industry giants, Intel and Fujitsu (www.fujitsu.com), introduced WiMAX solutions. The Intel product, PRO/Wireless 5116, is a highly integrated, IEEE 802.16-2004 compliant system on chip (SoC) for both licensed and license-exempt radio frequencies. The processor's radio features an OFDM physical layer with support for channel bandwidths up to 10 MHz, an integrated 10/100 media access controller, inline security processing, and a time-division multiplexing controller interface for handling applications such as voice over Internet protocol (VoIP). It also features adaptive modulation (BPSK, QPSK, QAM16 and QAM64) and offers a programmable architecture that makes it easier for equipment makers to add additional applications on top of the chip.

Fujitsu's solution, the MB87M3400 WiMAX SoC, is also 802.16-2004 compliant and was designed to enable deployment of BWA equipment for both base stations and subscriber stations in licensed or license-exempt bands below 11 GHz (Figure 1). It uses an OFDM 256 PHY that supports channels from 1.75 MHz to 20 MHz, and can operate in time division duplex (TDD) or frequency division duplux (FDD) modes with support for all available channel bandwidths. A programmable frequency selection generates the sample clock for any desired bandwidth. When applying 64 QAM modulation in a 20 MHz channel and using all 192 subcarriers, the SoC can sustain raw peak data speeds up to 75 Mbps; uplink subchannelization is also supported.

Of course, the first company to introduce an 802.16-2004-compliant WiMAX chip was WaveSat with its DM256 baseband IC. Today, the company offers a family of products built around DM256 for licensed and license-exempt radio frequencies. The Evolutive DM256 family features 5 bits/sec/Hz spectral efficiency, adaptive modulation, programmable channel bandwidth up to 10 MHz, and support for TDD, half FDD (HFDD) and FDD duplexing modes.

A handful of start-ups are also now making a play for the WiMAX space. One such company is Sequans Communications (www.sequans.com). Its SQN1010 and SQN2010 SoCs provide system vendors with comprehensive, integrated baseband solutions to build subscriber stations and base stations, respectively, for next-generation BWA networks.

Filling out the WiMAX ecosystem are announcements from companies like picoChip (www.picochip.com), which is now readying its next-generation flexible picoArray chip, with integrated ARM 926EJ-S processor, for availability next year. This 90 nm, CMOS device will allow carriers to build-out their infrastructure based on the 802.16-2004 WiMAX standard, as well as upgrade their equipment to support mobility once the 802.16e standard is complete.

In addition, the company just released a family of reference designs, including a PHY, MAC and RF radio with antenna, for both subscriber stations and base stations. The reference designs are aimed at fixed 802.16-2004 WiMAX, mobile WiMAX and WiBro; Korea's version of the WMAN standard. The new reference designs include PC6530 (for 802.16e base stations) and PC6620/6630 (for 80216d/80216e subscriber stations). The designs are compatible with all aspects of WiMAX specifications and are fully upgradable for new versions of the standard, as well as for advanced features such as the active antenna system (AAS) and multiple input, multiple output (MIMO) system.

Even test and measurement vendors, like Agilent Technologies (www.agilent.com), have gotten onto the WiMAX bandwagon (Figure 2). Its digitizers, spectrum analyzers and Advanced Design Systems (ADS) simulation tools help designers cut through the complexity of the WiMAX specification and better understand where and how problems may arise (see “Library speeds design of BWA applications,” p. 15). To help designers maximize their success in WiMAX, the company hosted an e-seminar entitled “From fixed WiMAX 802.16d to mobile 802.16e: RF and digital baseband testing.” The event featured information on the new measurement and test/troubleshooting approaches that will be needed to deal with the added layers of complexity 802.16e creates. The contents of the seminar can still be accessed at www.get.agilent.com/vmx_link.cgi?site=nammo_edm&code=3390_reg&ref=3390_eSem_Sept15_OFDMA_FE_reg_E.

Add to these announcements the fact that manufacturers like Airspan, Alvarion, Proxim, Redline Communications and SR Telcom, have plans to announce WiMAX devices. Cou-ple this with the work this year by service providers to begin commercial WiMAX trials and it's easy to understand why the WiMAX standard has, and will continue, to gain momentum in the months and years ahead.