There’s still lots going on in standards task forces,
but WiMAX presses forward even as some Tier 1s work on LTE.

WiMAX is a mobile communications protocol with an identity crisis. In stationary form, fixed WiMAX is catching on in emerging markets and for some business niches. On the other hand, mobile WiMAX still hasn’t seen the commercial light of day. That should be coming later this year with Sprint’s Xohm Project.

Other Tier 1 carriers in the United States such as AT&T and Verizon Wireless are committed to the 3GPP’s Long Term Evolution (LTE) alternative for wireless broadband, which won’t be ready to deploy until the 2010 timeframe.

But if you ask WiMAX supporters to cite the technology’s main advantages, they will point out that by the time operators commence LTE trials, the WiMAX standard will be on its second iteration, mobile WiMAX will surpass the fixed version in speed and availability, and the all-IP network may even be merged into the IPv6-based Internet of tomorrow.

The buck of WiMAX’s heavy lifting stops with Roger Marks, senior vice president for industry relations at NextWave Wireless and chairman of the IEEE 802.16 WirelessMAN Working Group, which includes 802.16d (fixed), the 802.16e-2005 amendment (mobile) and assorted ongoing projects. Marks believes both WiMAX and LTE have a place, and NextWave itself develops for both options, even though many industry experts think of the technologies as rivals. “Hopefully they grow toward each other, or they differentiate with markets and focus,” Marks says.

TASKS AT HAND
The IEEE working group that Marks works on has four current projects, according to Marks. They are the Task Group m, Relay Task Group, Maintenance Task Group and License-Exempt Task Group.

WiMAX today has maximum downlink and uplink speeds of 70 Mbps, but that is only at short range and in ideal conditions. Current WiMAX speeds in real-world use are about 10 Mbps-15 Mbps, with 20 Mbps-30Mbps being more likely as the networks and hardware improve in the next year or two, industry analysts say.

Task Group m is working on support for legacy equipment and on speeds closer to hundreds of megabits per second or even 1 Gbps. The group agreed to functions and performance levels last fall, and completed an evaluation methods document in March, to be submitted to the International Telecommunications Union by fall 2009. This version will operate in 20 MHz channels, compared to 5 MHz and 10 MHz channels for current WiMAX, Marks explains. That will basically double the speed of the connection.

“The Relay Task Group is trying to wrap up a standard that defines a relay station,” he continues. Current WiMAX equipment operates directly from devices to base stations, severely limiting its range and capacity. The standard should be finished this fall to allow multiple relay stations. Relays could be mobile, such as on a bus or train. The group is beginning to discuss how to make relays compatible with the 802.16m through the 16jm Ad-Hoc Group, he adds, so that the Task Group m’s speedier version of WiMAX will be backward-compatible with the relay station technology.

In the Maintenance Task Group, most of the topics are devoted to technical housekeeping, but there is discussion about improving the performance of WiMAX when used with frequency-division duplexing (FDD). Mobile WiMAX today uses time-division duplexing (TDD), which has half the spectrum requirements of FDD, but FDD may be more appropriate for voice calls because of its distinct channels for downlinks and uplinks. Both versions are supported in the specification.

Meanwhile, in the License Exempt Task Group, engineers are figuring out a specification for American 3.65 GHz-3.7 GHz support for WiMAX so that WiMAX can co-exist and avoid interfering with regulated networks and open-access frequencies. “Basically it’s kind of a listen-before-you-talk protocol,” Marks says. (Companies such as Alvarion already announced hardware for this purpose.)

Roger Marks: Both WiMAX and LTE have a role to play	Jeff Andrews: Suggests that SC-FDMA uplinks for WiMAX could be cheaper and reduce signal degradation.	Ron Resnick: Vigorously defends OFDMA uplinks.	John Saw: Mobile WiMAX is anything but an easy upgrade.	Jeff Thompson: Testing mobile WiMAX modems for MIMO support and beamforming.

UPLINK STRATIGIES
A somewhat controversial, unofficial topic for WiMAX’s future is the opportunity to reconsider its uplink scheme. WiMAX uses OFDMA in both directions, and in LTE technology there is a single device-to-base uplink called SC-FDMA, with OFDMA for the downlink. SC-FDMA is believed by some experts to be the more efficient option, as it can cost less and reduce signal degradation, despite issues related to out-of-band interference and backward compatibility, says Jeff Andrews, author of the book Fundamentals of WiMAX and an assistant professor at the University of Texas-Austin.

Ron Resnick, chairman and president of the WiMAX Forum, strongly defended OFDMA uplinks. “It’s true there’s a single carrier on the uplink, but when you look at the whole link budget... it balances itself out, there isn’t much of a difference. What you gain in the uplink, you lose in the backend, in the receiving side of the base station,” he says.

Marks, however, says it’s not so straightforward. “802.16 looked at this technology years ago… and some participants would like to go that way,” he acknowledges. Even though the Task Group voted to use OFDMA as a mandatory uplink method for 802.16m, it is possible that SC-FDMA could still be an optional method, he explains.

FIELD TRIALS
In the field, the fixed WiMAX standard found its ways into 260 commercial deployments in 110 countries so far, according to the WiMAX Forum. Trials of mobile WiMAX are just beginning to bring feedback from customers. Clearwire, for example, is conducting a “small trial” of mobile in a 168-square-mile area around Portland, Ore., mostly for Intel employees, company officials say.

Clearwire Chief Technology Officer John Saw emphasizes that mobile WiMAX is not an easy upgrade – “We are putting up sites and we’re running some tests. It’s like everybody loves sausages, and nobody wants to know how it’s made,” he jokes. “I don’t see any showstoppers or challenges with regard to the technology per se, but we are spending a lot of time fixing the bugs. We are spending a lot of time optimizing the network,” he adds.

Most of the bugs are low-level issues related to parameters and settings, such as thresholds and adaptive modulation. There also are handoff issues, and Clearwire works closely with equipment vendor Motorola. None of the issues so far required Clearwire to go back to the IEEE for help, Saw says. Another factor is that mobile WiMAX needs most of its backhaul bandwidth planned in a network design stage, compared to traditional cellular networks in which capacity can be configured after the construction begins, he says. Clearwire manages its current fixed WiMAX network in mesh and ring styles using off-the-shelf SNMP tools and plans to continue that in mobile markets.

Clearwire’s upcoming beta tests for mobile WiMAX will launch by the end of this year in Las Vegas and Atlanta, Saw says. Grand Rapids, Mich., is also on the agenda. Typically these tests are for a small number of customers who are technically savvy enough to report any problems back to Clearwire, company officials say. Next year, the company will consider offering femtocells and picocells.

Besides Clearwire’s mobile WiMAX trials and Sprint’s Xohm project, mobile WiMAX is also being used as a stationary upgrade to fixed WiMAX deployments. Although WiMAX provider Towerstream isn’t currently planning any mobile services, it’s still testing mobile modems because they have MIMO support and beamforming, plus the thorough upgrade path, CEO Jeff Thompson says. “What Towerstream is using WiMAX for is to replace the last mile… we can install in days, we don’t have to go through all these provisioning cycles, we’re not as beholden to the phone companies,” he says.

A trend he would like to see is tighter integration from the companies that make WiMAX chips and modems. WIMAX, Wi-Fi and SIP should all be integrated into one package, which would simplify installations and give end users a simple path to VoIP services, he says. Chip companies such as Beceem, Sequans and Texas Instruments disclosed similar plans recently, but fully integrated products aren’t due until later this year or next year, officials from those companies say.

Fernando Canelas, IT manager at Shake-A-Leg Miami, purchased Towerstream’s service to complement his T1 from AT&T’s former BellSouth unit. Shake-A-Leg is a non-profit organization bringing water recreation to disabled and underprivileged children, and its Internet access is mission-critical for running administrative and educational software. “Our grants depend on that. Another angle is, as a non-profit, we’re obviously on a limited budget. Any time there’s a hurricane, we have to worry about our recovery capability,” he says.

“We were looking for an alternative to the T1 that would be independent of the AT&T/BellSouth drop. If I were to go out and source a T1 from an alternative carrier, it would still come from the same drop. We have had problems,” he explains. After finding out that Towerstream offered fixed WiMAX in the area, Canelas was immediately interested.

“We went live in September of last year. We are pretty much getting twice the bandwidth compared to a traditional T1 carrier for the same money,” he says. “It’s worked out without a hitch. We’ve only had one outage.”

Canelas says the prospects for mobile WiMAX appeal to him, because Shake-A-Leg offers some activities on an island in Biscayne Bay, where his Wi-Fi antennas do not reach and do not support enough bandwidth for the desired streaming video application.

Mobile WiMAX may not be the easiest upgrade for carriers, which is one reason most experts agree that WiMAX of any form is best-suited for specialty purposes and emerging markets. But from the standards side and the equipment suppliers, the technology is making impressive progress, even as mainstream carriers largely ignore it. Whether that’s enough to make WiMAX a long-term success remains to be seen.