"In order to achieve even an 18% saving, the network would have to reuse the core network, backhaul, Tx and full site and antenna system," he adds. "Crucially, this network would offer no roaming capability and no voice fallback. All upgrades would have to be software-based and the implications would be significant."
Ovum's Grivolas adds that even if a given Wimax operator has the right equipment and spectrum amount to support a smooth RAN software upgrade - which won't always be the case - that software upgrade doesn't apply to devices.
"All of the devices will not be able to evolve their software, so there will be a huge spend there to subsidize new devices," he says.
In any case, he adds, with the Wimax Forum continuing to champion Wimax, as well as vendors like Alvarion who are focused primarily on Wimax, Wimax as a technology isn't going anywhere. "I don't believe that in 2015 there will be no Wimax networks."
Phillip Solis, practice director at ABI Research, notes that while vendors are indeed working to enable Wimax/TD-LTE migration, as well as dual-mode Wimax/TD-LTE chipsets, the migration message is more for the benefit of investors than operators.
"Investors are seeing TD-LTE making lots of headlines, which makes them look at Wimax operators and ask, 'Why should I invest in you when you're running Wimax?' So operators can say, don't worry, we're covered, we can make the switch if we need to. It's like insurance, which is actually good for Wimax because operators and investors are more likely to take a chance on it if they have that switchover option later."
That said, Solis adds, the Wimax and LTE landscapes will be complicated by fragmentation between FDD, TDD and related spectrum bands, which will make dual-mode ambitions difficult, and that will work against TD-LTE.
"People are assuming a lot of market synergies around TD-LTE that actually don't exist," he says. "It's complicated, but you've got LTE development going on for FDD and TDD, then there's all this band fragmentation with 4G, because you've got 2.6 GHz, refarming in the 3G bands plus backward compatibility, and digital dividend spectrum coming up," he says. "And in some markets like the US, you'll need multi-mode support for EV-DO in all that, and in China, TD-LTE chips will be TD-LTE/TD-SCDMA chips. Software-defined radios help and bigger RF front ends help, but you'll still see a lot of fragmentation that applies to TD-LTE."
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