Faster Wi-Fi has moved two steps back, after a key standards meeting knocked the leading proposal back and re-opened the debate to rivals.

The TGn Sync proposal needed a 75 percent majority in this week's meeting of the IEEE's 802.11n task group, to become the eventual IEEE standard. Instead, the Intel-backed standard dropped back below the 50 percent majority in won in the last meeting, so the debate is opened up again.

At the last meeting in March TGn Sync got enough to be the leader, but not the winner. Earlier this week, TGnSync members, fearing their support had waned, moved to adjourn this week's meeting in Queensland, Australia, without taking a second confirmation vote on the group's 11n technology proposal.

The adjournment was rejected yesterday, and the group took the confirmation vote. Under IEEE rules, a proposal like this must win 75 percent of the vote to be accepted as the basis for a draft standard. At the first confirmation vote, the TGnSync plan won backing from 57 percent.

This week, the plan failed to get even a majority: only about 49 percent of those present voted for it.

That setback means the chief alternative plan, from a second vendor group called World-Wide Spectrum Efficiency (WWiSE), whose backers include Airgo, the leading MIMO chip vendor, can now be reconsidered, along with the TGnSync plan.

Both plans are based on a technology called multiple-input/multiple-output (MIMO), which proponents say will boost WLAN throughput to over 300Mbit/s, though the standard will call for a minimum of about 100Mbit/s. That compares to today's 802.11a and 11g throughput of 20-24Mbit/s.

MIMO breaks up a radio transmission into two or more data streams within one channel. Each stream is sent, and received, by a separate antenna, and then recombined on the other end. The result is that much more data can be sent over the available radio spectrum than is possible with standard transmissions today.

The differences, advocates of both groups say, is in a variety of implementation details. One example is that TGnSync proposes increasing the channel size from 20MHz to 40MHz; WWiSE favours keeping the existing 20MHz size.

WWiSE is repeating calls for compromise, which it made after the last meeting. One member says the defeat of the TGnSync plan should persuade both groups to come together quickly on a compromise scheme that will win the 75 percent backing that's needed.

"My interpretation is that we have two groups with approximately equal support, and the way forward is for them to get together, get past some of the devisive issues, and come to the July IEEE meeting, or possibly the September meeting, with a joint proposal," says Jim Zyren, marketing director for the WLAN business unit of Conexant, a chipmaker in the WWiSE camp. "No one can get the 75 percent without a compromise."

But is a compromise technically feasible? "Absolutely yes," Zyren says. "The technical differences are not that great. I've seen other standards-making efforts, with much greater differences come together. If all parties realise that compromise is essential, then compromise becomes quite possible."

TGnSync members Agere, Atheros, and Intel have not responded to requests for comment.