Standards groups eye unified broadband wireless specs
By Loring Wirbel, EE Times
Jan 15, 1999 (12:10 PM)
URL: http://www.eetimes.com/story/OEG19990115S0012 

ORLANDO, Fla. — Developers took the crucial first steps this week in synchronizing global standards for all broadband wireless systems, from 5 GHz to 50 GHz and beyond, as standards bodies from the United States, Europe and Japan convened here. While strong differences of opinion persist over physical interfaces and data-link structures, the meeting advanced the goal of a common infrastructure between in-building wireless LANs and new, micro- and millimeter-wave broadband networks with a cellular-like infrastructure.

Wide-area schemes showed the strongest signs of convergence, though some wrinkles must be ironed out. Among local-area networks, separate U.S. and European wireless offerings continue to resist harmonization, and a nascent class of "personal-area" wireless links still occupies a relatively undefined spot at the fringes of interoperability.

The IEEE's 802.11 wireless-LAN working group and emerging 802.N-West broadband wireless-access group held its first joint meeting this week with the European Telecommunications Standards Institute's (ETSI's) Broadband Radio Access Network technical group. Representatives of Japan's Multimedia Mobile Access Communications council (MMAC) also attended.

802.N-West — named after the federal government's National Wireless Engineering Systems Testbed (Boulder, Colo.) — finished a project-authorization request specifying a Local Multipoint Distribution Service (LMDS) standard for 28-GHz point-to-multipoint broadband radio. The group plans to present the request to the IEEE 802 executive committee in March.

Meanwhile, the 802 committee has asked the group to prepare a second authorization request that would specify how multiple broadband radio systems would coexist.

Once the requests are submitted, the 802 group will likely dedicate an official IEEE working group to broadband. The executive committee found little dissent for giving N-West its own study group last November, raising N-West chairman Roger Marks' hopes that a formal working group could be created quickly.

The U.S. LMDS initiative and ETSI's HiperAccess project both assume a point-to-multipoint structure that would give urban and suburban consumers and businesses a multi-megabit Internet-access alternative to cable modems and digital subscriber lines. The Personal Communications Industry Association's Wireless Broadband Alliance group, which represents LMDS license holders, has expressed interest in working directly with the IEEE/ETSI broadband group, Marks said. But contentious issues persist.

One faction within the ETSI group made clear in the last week that it supports mesh topologies as well as point-to-multipoint, allowing more of a broadband any-to-any switching structure. Some 802.N-West members, seeking to include higher-frequency, long-distance rural radio links in the standard, object to the current "urban/suburban" focus.

Even the frequency bands remain open to question. U.S. members want standards that include more than the FCC's 28-GHz allocation, including the emerging 38-GHz band, while ETSI is looking at a range of possibilities between 24.5 and 43.5 GHz.

The European broadband group is expanding from its 5-GHz HiperLAN program in three dimensions. HiperLAN 2 will take 5-GHz in-building speeds from 13 to 25 Mbits/second; metropolitan architectures could provide at 25-Mbits/s; and 155-Mbit/s speeds are being examined over short distances to interconnect HiperLAN 2 and HiperAccess systems.

LMDS startup Ensemble Communications Inc. is chairing the core study group on air-interface definitions. Several group members expressed surprise at the FCC's failure to include hard definitions in the U.S. LMDS standard for such elements as channelization and "spectral etiquette" (access and backoff). Air interfaces must be broad enough to handle a range of modulation methods, and access policies must allow the transport of different traffic types with dissimilar quality-of-service parameters.

Beyond radioOn the analog side, the issues extend beyond the chosen bands for radio systems. Most in the IEEE study group support work in defining an indoor/outdoor intermediate-frequency (IF) open interface for the home access unit, and a special IF study group has been formed under Jack Van Der Star of Belstar Corp. But larger telephony- and cable-TV-transmission companies may prefer to keep home interfaces closed.

The ETSI broadband group and 802.N-West met this past week to determine where the two might collaborate on physical-layer functions. Jan Kruys, chairman of the ETSI broadband-access effort, said his group faces the added concern of handling interference issues with satellite-communications carriers. Most European Union nations have agreed on frequency sharing, but the U.K. Radio Commission and a few large satellite-system vendors may fight against frequency allocation by the ETSI group.

Meanwhile, the 802.11 expanded its current, 2.4-GHz standard in two dimensions, and a special Personal Area Network (PAN) study sought to determine whether it should remain inside 802.11 or request the creation of a dedicated working group to handle very short-range networks (used, for example, on the factory floor). If personal digital assistants become popular and the notion of a "desktop-area network" coalesces, the PAN group could aim for broad consumer applications. Members thus begrudgingly debated compatibility with the proprietary Bluetooth effort.

There are two efforts for updating the core 802.11 spec. The 802.11a effort seeks to achieve a range of 6 to 54 Mbits/s in the 5-GHz frequency band (24 Mbits/s is the primary target rate); 802.11b seeks to use advanced modulation and RF-access techniques to raise the speed of 2.4-GHz wireless LANs to ranges approaching 20 Mbits/s.

The former group met with ETSI broadband representatives to synchronize 802.11a with HiperLAN 2. Task-group chairman Naftali Chayat of Breezecom Ltd. kept the approval pace constant, getting the IEEE to change the number of its subcarrier channels from 48 to 52, for example, to mesh with the ETSI spec.

There still is a fundamental difference between 802.11 and HiperLAN 2, in that the former provides a best-effort service through a carrier-sense/multiple-access MAC like Ethernet, while HiperLAN 2 uses a time-division multiple-access/time-division duplex method to offer quality-of-service provisioning. The HiperLAN 2 data-link control layer can support Ethernet frames but is a connection-oriented topology, supporting such services as ATM. Limited harmonization between 802.11a and HiperLAN 2 may be the best that can be hoped for.

The 802.11b faced some opposition to the idea of maintaining backward compatibility with older frequency-hopping and direct-sequence LANs. In the end, a move backed by Aironet Communications Inc. and Lucent Technologies Inc. to take out hopper interoperability was defeated, but the warring camps met over the next two days to figure out better ways to interoperate with older, slower frequency-hopping systems. The groups have agreed on an 11-Mbit/s baseline spec with CCK modulation, said Harris Semiconductor's Al Petrick, vice chairman of 802.11.

The status of the so-called personal-area networks was still being debated at press time. Committee members will make a proposal to IEEE 802 for a formal program, though it could end up as part of 802.11 or as a working group in its own right. Chairman Ian Gifford of AMP Inc./MA-Com said the PAN group has defined a set of classes for interoperation with 802.11 WLAN devices.