Unfortunately, the path from fixed to mobile WiMAX is following the 802.11a example. During the development of 802.16e, which specifically addresses mobility, it became clear that the OFDM-256 PHY used in fixed WiMax could not meet the requirements of mobile applications. And unlike the 802.11b/802.11a situation, there was no installed base of fixed WiMax when this decision was made. Meanwhile, South Korea is leading the charge to mobility with WiBRO, which is expected to become a WiMAX profile under 802.16e. Service-provider KT plans to launch WiBRO service in April 2006 in the cities of Seoul and In-Cheon. Korea is expected to have about two million WiBRO subscribers in 2007, growing to nearly 10 million in 2011. With mobile WiMAX stealing the spotlight, where does this leave fixed WiMAX? Overshadowed But Not Forgotten Because the WiMAX fixed and mobile PHYs are fundamentally incompatible, the two versions will be deployed in different applications. Broadband wireless access (BWA) is one application touted for fixed WiMAX. WiMAX evangelists would have you believe fixed WiMAX can deliver triple-play (voice/video/data) services, just like DSL or cable. But a WiMAX channel is a shared medium, and current profiles for licensed bands deliver a maximum downlink speed of 26Mbps at the PHY layer. After MAC overhead, WiMAX can carry perhaps three standard TV streams or a single HDTV stream. This bandwidth is not enough for a single home, much less a large number of subscribers. Although it is unlikely to compete directly with DSL and cable, WiMax will be an attractive alternative where no DSL or cable-modem service is available. In rural areas of China and India, for example, WiMAX could deliver voice and data services without the need to lay copper or fiber cabling. WiMAX equipment can be installed at one location in a community, and other technologies such as Wi-Fi can be used to distribute services locally. In this way, the relatively high cost of the WiMAX equipment is amortized across many users. Fixed WiMAX is also attractive as a backhaul technology for cellular networks, allowing new cell sites to be installed in rural areas without cabling. WiMAX can also upgrade existing cell sites that served by copper T1/E1/J1 lines, which are becoming a bottleneck for 3G data services. In some areas, WiMAX could be less expensive than running fiber to these sites. WiMAX Chips Ease Equipment Designs What makes fixed WiMAX attractive for equipment designers is the availability of application-specific chips. A number of vendors offer system-on-chip (SoC) products that implement OFDM-256 baseband and 802.16 MAC functions. A separate set of vendors offers WiMAX radio transceivers for various bands. Intel is a high-profile supporter of WiMAX, and the company was first to market an SoC device. The PRO/Wireless 5116 integrates all of the digital functions for a fixed-WiMAX CPE design. The highly programmable chip includes a pair of ARM9 CPUs for MAC and upper-PHY processing as well as a DSP for the modem. A 10/100 Ethernet port provides the connection to a PC or router. Fujitsu is the second major chip vendor to offer a WiMAX SoC. The SoC includes a pair of CPUs for the MAC function, while the modem is implemented in hardware. Like Intel’s chip, Fujitsu’s MB87M3400 can be used as the heart of a CPE design. Unlike Intel’s chip, the Fujitsu device can also be used in base-station designs. In this case, the MAC software runs on an external processor. French startup Sequans Communications sampled its first chip in September 2005. The company’s WiMAX SoC provides a number of features not found in the Intel and Fujitsu designs. Wavesat offers a WiMAX PHY chip plus MAC intellectual property. PicoChip Designs offers a software-defined PHY implementation running on a massively parallel DSP chip. WiMAX-specific radios are now available from both large and small vendors. Texas Instruments offers chips for all three WiMAX bands: 2.5GHz, 3.5GHz, and 5.8GHz. Radio specialists RF Magic and Sierra Monolithics (SMI) were the first vendors to offer merchant WiMAX radio chips. Better known for Wi-Fi power amplifiers, SiGe Semiconductor now offers WiMAX transceiver chips as well. Using these commercially available devices, OEMs and ODMs can design fixed-WiMAX equipment with relative ease. This approach allows the equipment vendor to focus on designing equipment to meet a specific need. Even low-volume applications can be targeted due to the moderate cost of developing a complete system. Thus, these highly integrated chips will enable fixed WiMAX to find a home in many different applications.
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