By Tara Seals

While the first WiMAX-certified products arent expected until later this year, some supporters of the 802.16 standard are paving the way for industry maturation now. Spearheaded by hotspot aggregator RemotePipes Inc., the fledgling WiMAX Global Roaming Alliance (WGRA) aims to make seamless interoperator roaming for mobile, broadband wireless data as ubiquitous as cellular roaming is for voice.

The new working group, which includes vendors, service providers and others in the WiMAX supply chain, has the mission of using available standards to create an open roaming framework for WiMAX service providers, including streamlining authentication and accounting functions between networks and other OSS areas.

The likelihood of a single or even two or three carriers to provide a global WiMAX offering is slim, says Eric Engbers, chairman of the WGRA and president of RemotePipes, which now is offering its IPRoamer aggregation platform to pre-WiMAX operators. We need to ensure the prerequisites for roaming are built in as these networks are deployed, because you must address ubiquity if advanced wireless applications are going to be useful. We need disparate networks and spectrum running as one.

While roaming is ostensibly the swapping of traffic by network operators in return for compensation, it is not quite as simple as it may sound. This could develop in a similar way to the cell model, says Olivia Hecht, director of marketing for Airpath Wireless Inc., WGRA member and maker of the InterRoam product, which provides a technologyagnostic clearinghouse model for wireless operators to forge roaming agreements. However, cellular technology is in rationalized licensed spectrum and there are only a handful of providers. We dont know how WiMAX will shake out.

Aside from the fact that the 802.16e mobile WiMAX standard is yet to be ratified, there are many unknowns, the largest being spectrum allocation. The rationalization and liberalization of the spectrum in line with what this technology is capable of is the toughest nut to crack, notes Bob Syputa, an analyst with WiMAXPro.com.

The questions of whether providers will operate in licensed or unlicensed spectrum, and of spectrum availability, hang like a specter over the birth of WiMAX. While the initial nonmobile 802.16 standard is set, and gear is being built to spec, operators in the rest of the world, at least as it stands now, will be speaking on a different wavelength from those in the United States literally.

Due to the lack of an available and appropriate global band, regulators have allocated various licensed and unlicensed bands for WiMAX in different countries. In many parts of the world, 2.5GHz and 3.5GHz are the bands of choice. However, 3.5GHz is unavailable in the United States, prompting the FCC to open up the nearby 3.6GHz band, along with unused MMDS broadcast television spectrum. Meanwhile, the WiMAX Forum is fighting it out with 3G operators in Europe over the use of the 2.5GHz band. As regulatory battles continue around the globe, WiMAX is contending with a splintered spectrum picture that will likely encompass 2.3GHz, 2.5GHz, 3.4-4.2GHz, 5.4GHz, 5.8GHz and others. Most WiMAX-certified, interoperable equipment will function only in one or two of those bands initially, meaning that some countries will be left out in the cold. Eventually, a global WiMAX handset or device will require a laundry list of embedded radio functionality an expensive proposition for manufacturers. Or, users will have a portfolio of hot-swappable device cards.

Meanwhile, some WiMAX operators will choose to operate in unlicensed spectrum, which will lower their cost of entry. Like Wi-Fi, license-exempt WiMAX could be used to create private, ad hoc networks for enterprises, colleges, municipalities and others. Tying together the potential explosion of these single-use networks with those of licensed operators provides an additional challenge for seamless roaming. With Wi-Fi we have seen a hotspot aggregation model to effect roaming, says Hecht. We may see the same in unlicensed WiMAX world, but it doesnt answer the question of roaming to the public licensed operator networks and the commercial agreements required there. It also makes for complicated OSS and settlement layers. Another unknown in the roaming arena is the use case for WiMAX. Depending on the cost versus coverage equations at play as well as consumer uptake, WiMAX may make the most sense as a last-mile broadband solution for the underserved or for individual municipalities. This would render roaming between WiMAX networks a moot point. The real goal in that case will be a world where 4G, WiMAX, proprietary and Wi-Fi networks capable of carrying voice and data are tied together in a seamless shroud of connectivity. Devices will automatically connect to the strongest signal and transition between networks as necessary, with everyone being appropriately compensated in the process.

For now, enabling WiMAX operators to swap traffic seamlessly among themselves is the first step, but Engbers acknowledges WGRA is taking the long view. Ubiquity is the underlying requirement for the adoption of any technology, he says. It will be a long time before we get to that, but we want to start working on it now, before the networks are deployed and its too late to go back and fix expensive errors.