Network equipment maker Airspan and operator Freedom4 have shown a laptop roaming seamlessly between WiMax networks on different spectrum bands. The companies say this will help operators build credible WiMax networks using limited radio spectrum, and give users an alternative when 3G networks run out of steam.

"To have a high capacity WiMax network in a market such as the UK, you need devices to do what ours does," said Graham Currier, chief operating officer of Freedom4, formerly known as Pipex Wireless. In the UK's much-delayed 2.6GHz spectrum auction, operators may only get 30 or 40MHz of spectrum, he said, which would not be enough to deliver the kinds of sustained data rate that users will expect. Dual-band roaming would allow these operators to buy wholesale data from other operators (in particular Freedom4, which has a large block of spectrum around 3.6GHz) and move users onto that spectrum as required.

Dual-band WiMax dongles are already available, but the Airspan demonstration shows that users can be placed on different spectrum under the control of the network operator, Currier explained: "We must consolidate lots of spectrum, to allow a network that delivers the kind of capacity. You need one device that can move to other spectrum without the awareness of the customer."

"This capability changes the ground rules for carriers," said Paul Senior, chief technical officer at Airspan. "Any prospective WiMax carrier can now create a large spectrum allocation for their deployment by combining smaller pieces of spectrum in different bands. This also allows carriers the ability to use larger allocations of spectrum per cell site (say 60 MHz, or even 120 MHz), and create sites with 100-200 Mbit/s of wide-area mobile broadband capacity."

"This would be roughly ten times the capacity of a typical 3G HSPA site," said Senior.

The technology should make European roaming easier said Currier: "Europe has a lot of historic, odd spectrum, and is very fragmented. If you want to have Europe-wide data mobility, almost every network has to work like ours."

Currier backed the comparison with 3G, saying dongles have failed to deliver the 7Mbit/s they promised, and yet they are still overloading the network: "The problem with 3G is in the air and the backhaul. The network was built for narrow band, and now users are downloading Doctor Who from iPlayer, on what is essentially a voice network. In London my calls have started dropping, and on the motorway, my phone drops calls between cells. Two years ago that didn't happen."

"I'm predicting that next year is going to see some fairly ugly examples of mobile broadband 'capacity crunch'," predicted Dean Bubley of Disruptive Analysis on his blog. "And given that capex budgets are going to be a bit thin, I reckon we'll see quite a few more dissatisfied customers."

Freedom4 still only has a trial in Stratford-on-Avon, and networks rolling out in Manchester, Milton Keynes and Warwick. The company is negotiating with Ofcom to change the conditions of its 3.6GHz fixed wireless licence to allow mobile WiMax. Despite this, Currier is confident he will have commercial service that can beat the mobile operators' 3G, and LTE when it arrives.