One of the most confusing parts of Clearwire’s long-term evolution announcement Wednesday was its plan to deploy an "LTE-Advanced ready" network. Clearwire itself stuck the term in quotation marks in its press release as if to imply that it was open to interpretation. In an interview with Connected Planet, Clearwire Senior Vice President and CTO John Saw explained what exactly the mobile broadband operator means by "LTE-Advanced ready" as well as expanded on the details of its future LTE rollout and strategy.

Clearwire will deploy a network in such a configuration that when LTE-Advanced devices are available it can easily turn on the capability, Saw explained. The LTE-Advanced was ratified earlier this year as part of the 3GPP’s Release 10 set of standards, but it will take years before the chipsets and devices supporting LTE-Advanced are available. Clearwire, however, wanted to ensure it was ready for that moment so it could immediately tap into the technology’s enormous bandwidths, Saw said.

One of the biggest advantages LTE-Advanced has over plain old LTE is the ability to aggregate carriers into huge-bandwidth pipes. Clearwire will deploy multiple 20 MHz carriers—the largest permitted under the current LTE standard—on contiguous spectrum. When LTE-Advanced software is available and the first devices capable of receiving its bandwidth are released, Clearwire can then bond those carriers together.

The result will be a network with some of the fattest pipes in the business, and one with unparalleled capacity. LTE-Advanced will let Clearwire deploy not just one 40 MHz carrier but multiple 40 MHz carriers. Clearwire has more than 100 MHz of 2.5 GHz of spectrum in all of its markets, but in the largest markets its holdings go all the way up to 160 MHz. That means in some of the largest markets Clearwire could deploy four 40 MHz carriers if it were to phase out WiMAX. To put that in perspective, AT&T’s proposed mega-carrier, built by combining its own and T-Mobile’s advanced wireless service (AWS) spectrum, also would total 40 MHz, while Verizon’s current LTE networks runs off of 20 MHz of 700 MHz spectrum.

Technically Clearwire could aggregate even more carriers than two, creating pipes 80 MHz, even 100 MHz wide as permitted under the standard. It’s one of the only operators globally with the spectrum holdings to attempt such a feat. But Saw said the larger the carriers become the more demands they make on the radio amplifier. Anything beyond 40 MHz quickly becomes infeasible, he said. "Though I have learned in this industry there is no such thing as too much capacity,” Saw said. “The customer always scales his use to what’s available."

Clearwire also believes it can make much better use of spectrum through its choice of a network configuration. While every U.S. operator is deploying LTE in a frequency division duplexing (FDD), which splits the uplink and downlink into separate channels, Clearwire opted to stick with the time division duplexing (TDD) configuration of its WiMAX network. TDD uses the same spectrum for uplink and downlink, allowing Clearwire to dynamically allocate more capacity to path depending on how the network is being used.

Saw said that will be of tremendous benefit as LTE-Advanced is introduced. Clearwire expects demand to increase for both higher downstream and upstream bandwidths, but not at the same rates. There will be a much bigger need for more downlink capacity driven by DH streaming video and other content, he said. "We’re already finding that customers use the network asymmetrically," Saw said. "With TDD, we can adjust the ratio of uplink and downlink capacity based on our customers’ behavior."

There are other advantages to using a TDD configuration, though, the biggest of which are deployment cost savings and the ability to use every megahertz of its spectrum, Saw said. In its LTE trials, Clearwire tested TDD and FDD configurations (CP: Clearwire paving the way for 100 Mb/s). In the case of FDD, Clearwire created an artificial guard band between the uplink and downlink channels. Clearwire ultimately chose TDD, however, because it would allow it to re-use much of its existing WiMAX infrastructure, Saw said. Its WiMAX antennas and radios could pull duty for the LTE network, and on the base station side, Clearwire could easily upgrade to WiMAX with software, adding more baseband processing line cards to support LTE’s new capacity, Saw said. Furthermore, Clearwire wouldn’t need to implement a guard band with TDD, permitting it to deploy an uninterrupted succession of LTE carriers across the 2.5 GHz band, Saw said.

Sticking with TDD, however, puts Clearwire outside of the mainstream in the U.S. where all operators are adopting FDD systems. Even Clearwire’s majority owner and primary partner plans to deploy an FDD LTE system as part of its network sharing deal with LightSquared (CP: LightSquared sees no obstacles left to building LTE network). By being the odd man out, Clearwire won’t be able to sell the FDD devices that vendors build for other U.S. LTE operators. But Saw pointed to the huge range of frequencies being used for those FDD deployments—due to their different 3G technologies and different LTE bands most operators globally won’t be able to share devices.

Furthermore, Clearwire is tapping into a larger TD-LTE ecosystem. China Mobile, Softbank in Japan and numerous other international operators are deploying TD-LTE in the bands between 2.3 GHz and 2.7 GHz—making it the closest thing to a common global LTE band in the world, Saw said. Chipset and device makers will be able to build a sizable ecosystem around that band, which ultimately benefits Clearwire’s wholesale customers. Clearwire’s ultimate hope is that TDD deployments become so common, that device makers will embed both TDD and FDD radios into all devices.

"We want to make the 2.3-to-2.7 chipset so cheap and so common that whenever we find a customer who wants to use LTE it will be easy for them to get their hands on it," Saw said.

While Clearwire is readily forthcoming about the technical details of its deployment plans, the strategic details are a little cloudier. Clearwire has no launch date for LTE. In fact, it won’t even start building the network until it gets more funding. Clearwire estimates it needs only $600 million to do the initial LTE upgrade in markets with the most data demand, but right now that’s $600 million it doesn’t have.

Saw said he couldn’t provide any details on how many markets or how many cell sites would get that first wave of LTE networks, but he was able to share the strategic approach Clearwire would take to that deployment. Clearwire doesn’t plan to build out entire markets with LTE—at least not at first. Instead, Clearwire will identify the most heavily trafficked cell sites on its WiMAX network and target the LTE deployment in those high-volume zones. That approach won’t give it a complete LTE network in the markets it deploys in, but Clearwire isn’t looking to provide end-to-end LTE coverage, Saw said. Rather, the operator plans to wholesale that capacity to other LTE operators looking to augment their networks in high traffic areas. It can also offer a combination of LTE and WiMAX to its existing mobile virtual network partners, Saw said.

Eventually the LTE network will expand to cover whole markets and the rest of the country as funding becomes available. At that point, Clearwire will investigate other strategies, Saw said. While building overlaying LTE on its current WiMAX footprint is definitely the cheapest alternative, new markets would require new networks. Saw said Clearwire would revisit the idea of a network-sharing partnership with Sprint when it gets to that stage of its expansion.

"Networking hosting opportunities like Network Vision are much more conducive to an operator that doesn’t already have a network," Saw said. "We’re in discussions with Sprint to use their networks in markets where we don’t currently offer service."