Fixed wireless access rides wave of support

Despite the much-publicized demise of fixed broadband wireless access (FBWA) providers such as Winstar and now XO Communications, and the cessation of rollouts by Sprint and Worldcom, the FBWA market is alive and well, thanks to a ground-swell of support for wireless Internet service providers (W-ISPs) operating in the unlicensed bands.

Though much maligned for their susceptibility to interference, W-ISPs and their equipment providers are riding a wave of popularity unrivaled by even the most ambitious licensed multichannel-multipoint distribution service or local multipoint distribution service (LMDS) projects. Contributors to this week's In Focus section explore the benefits and limitations of FBWA systems and detail what hurdles must be cleared to build interoperable systems.

Attractive for their low cost of entry, the unlicensed FBWA W-ISPs range from the rogue IEEE 802.11b-based networks run on a no-fee basis by rebellious inhabitants of inner-city tenement blocks, to fully fledged equipment providers and their customers targeting networks in the 2.45- and 5-GHz ISM and U-NII bands, respectively. All are jockeying for a share of the 300 million broadband business and residential premises that U.K.-based research firm ARC Group (www.arcgroup.com) predicts will be connected via myriad broadband-access technologies by 2007.

The low cost of operation at 2.45 GHz is a result of high volumes of 802.11b equipment and the relative ease with which these networks can be set up. This has led to the "organic" growth of W-ISPs, which flies in the face of the organized, licensed, top-down approach taken by Sprint and Worldcom. Both of those halted their rollouts, citing high equipment costs and poor performance. Both are waiting for next-generation equipment with improved line-of-sight capabilities before proceeding any further.

For its part, LMDS systems operating at above 10 GHz, which were originally intended for high-data-rate last-mile wireless access, are being relegated to cellular back-haul applications. According to Michel Peruyero, product-line director of Alcatel's Fixed Wireless Division, LMDS is now even being deployed as a WLAN backhaul option, such is the penetration WLANs.

Leading the effort to drive 802.11x technology into the wide-area-network space is XtraTyme Technologies (Hutchingson, Minn.), led by founder and CEO Kyle Ackerman. Under the auspices of its Blueprint America Project, Xtratyme is implementing what it calls its ten-step plan that can be followed by community leaders to get 802.11x-based high-speed Internet access deployed in their locale. "Microwave technology, specifically 802.11x, has allowed a company such as ours the opportunity to develop a solution that was not before economical nor practical," Ackerman said.

While 802.11x WLAN-based radios can be adapted for the wide-area network, the technology was not specifically targeted for that application and hence faces many obstacles. Aside from the obvious security issues — many of which can be overcome through judicious use of virtual private networks and firewalls — the technology also faces signal propagation and media-access complications, as Naftali Chayat, chief scientist at Alvarion explains in his contribution. According to Chayat, WLANs are designed for indoor applications over short distances, hence echoes from signal bounce are much shorter — tens of nanoseconds — than in the outdoor environment — hundreds of nanoseconds to a few microseconds.

As for media access, argues Chayat, WLAN systems' packet structure is too long to support voice and also must contend for access with other users. Alvarion has augmented the core 802.11x technology to overcome these obstacles to allow optimum operation in both unlicensed and licensed bands.

But therein lies the problem for the many equipment vendors deploying such networks. With proprietary adaptations, the interoperability of equipment, which is so vital to lowering the cost of equipment, vanishes. Recognizing this possibility, the IEEE 802.16 Working Group on Broadband Wireless Access has developed a set of physical-layer and media-access-controller (MAC)-layer standards for FBWA.

According to chairman Roger Marks, the IEEE 802.16 Working Group's particular focus is on the 2- to 11-GHz bands of operation. The IEEE 802.16a rules stipulate the use of single-carrier, multiple carrier (OFDM) and orthogonal frequency-division multiple access (OFDMA) in the licensed bands, and OFDM in the license-exempt bands. The choice of OFDM, which results from that technology's relative immunity to multipath interference, will allow OEMs to directly leverage 802.11a and 802.11g equipment when that standard is ratified.

All of the work being done under the 802.16 WG will be supported by the WirelessMAN MAC, according to Marks, which will support both fixed and mobile devices, "with a forward-looking and flexible design that holds the promise of future multitiered wireless metropolitan-area networks." Flexibility includes adaptive modulation, frequency control and support of frequency-division multiplex and time-division duplex systems.

So, while much FBWA development and deployment is taking place free-range style from the bottom up, it might well take the standardization efforts of the IEEE to fully realize the low-cost potential of WLAN adaptations for the wide- and metropolitan-area network.