Research firm Ovum offered Clearwire some good news today with a report predicting TD-LTE will go "mainstream" over the next four years, with 25 percent of all LTE connections forecast to include TD-LTE by 2016.

Clearwire is banking on TD-LTE, which runs in unpaired spectrum instead of the paired spectrum used in AT&T and Verizon Wireless' LTE deployments.

Getting more operators than just itself will be critical to the success of Clearwire's TD-LTE service, or the technology will become a niche product with a smaller, more expensive line of smartphones than its larger competitors.

Growth is expected to come not just from the United States and China, where China Mobile is working on a TD-LTE network, but also from operators in Japan, the Middle East and Europe. Japan's Softbank, Australia's Optus, Hi3G in Sweden and Denmark, India's Bharti Airtel, and STC and Mobily in Saudi Arabia are moving forward with TD-LTE, sometimes in combination with FD-LTE, the version that uses paired spectrum.

These operators will serve as major drivers of TD-LTE, pushing down handset and equipment costs and making devices more widely available. ZTE recently announced it would have a TD-LTE smartphone by the end of this year.

Daryl Schoolar, a principal analyst in Ovum's Network Infrastructure practice, said in the report that operator demand would push vendors to step up production of TD-LTE products. ZTE recently announced it would have a TD-LTE smartphone by the end of this year.

Clearwire doesn't expect to light up its network until the middle of next year, when it plans to turn on 5,000 TD-LTE cell sites in 31 cities, including New York City, San Francisco, Los Angeles, Chicago and Seattle. It will eventually expand its TD-LTE service to a total of 8,000 cell sites and has not ruled out further expansions.

The network will overlay Clearwire's existing WiMAX infrastructure. Instead of broad coverage, Clearwire is deploying its TD-LTE network in what it calls "hot zones," high-traffic areas in urban centers.

It plans to sell capacity on its network to other operators looking to offload traffic from their own LTE networks. Sprint and Leap Wireless International have already signed up for the service, and Clearwire's executives have said they're working to get contracts with other operators.

President and CEO Erik Prusch said at an investor conference last month that Clearwire has not ruled out potential TD-LTE customers who are primary competitors of Sprint, such as AT&T. Sprint is both Clearwire's largest customer and largest shareholder, though it no longer holds a majority stake in the company