Sprint (NYSE: S) is jumping into LTE Advanced (LTE-A) carrier aggregation later this year as part of its Sprint Spark initiative, and the operator is also taking hard looks at numerous other cutting-edge technologies, such as SON and even Cloud RAN, for inclusion in its long-term roadmap, said a top executive.
"Historically we've looked to technologies a bit differently than everyone else. We're the only ones deploying TD-LTE. We're the only ones deploying 8T8R," observed Ron Marquardt, vice president of technology for Sprint technology innovation and architecture.
That willingness to stand out from the crowd means technologies that other U.S. operators may not consider could find a home at Sprint.
"We're evaluating everything from CoMP (coordinated multipoint) to even Cloud RAN on the more speculative end, just because of the backhaul requirements for that," Marquardt told FierceWirelessTech.
Advanced self-organizing network (SON) technologies, enhanced inter-cell interference coordination (EICIC), high-order MIMO options and other advanced antenna systems "are all under consideration," Marquardt added.
"We're actively investigating all sorts of SON options--architectures as well as specific implementations," he noted, though cautioning that "we're not even close to making any decisions, much less any announcements."
Marquardt, who was VP of technology development at Clearwire before joining Sprint, heads a team looking at longer term roadmap issues outside the plan of record, meaning researching options and tradeoffs for technologies that might start being deployed 15 to 18 months out. "Not everything we do ends up coming to fruition," he said.
As Marquardt noted, one example of a network architecture that may or may not be employed at Sprint is Cloud RAN (radio access network), which is also referred to as Centralized RAN or C-RAN. The approach leverages distributed base station architecture and comes with hefty backhaul requirements.
"Cloud RAN provides a lot of interesting capabilities to limit interference between sites and coordinate the most efficient use of spectrum," Marquardt said.
"You have to remember that we are majority-owned by Softbank, and Softbank and other Asian carriers, in addition to Sprint, are major partners in GTI (Global TD-LTE Initiative). And a lot of the TDD technologies being deployed in Asia are also being deployed with Cloud RAN, where it's admittedly much more cost effective given the geographies there and the density of people in many of the major cities," he continued.
But Marquardt argues that does not mean C-RAN must be restricted to Asia. "I want to emphasize that some of these technologies are potentially possible here if we can crack the code on the right backhaul scenario. I don't think that's something you're going to see anytime soon, but I don't think that's something we're going to write off and just say, 'It's not going to be possible in the U.S. market,'" he said.
Sprint Spark is the operator's tri-band 800 MHz/1900 MHz/2.5 GHz LTE service, which will initially aggregate two 20 MHz TD-LTE carriers in the 2.5 GHz band to deliver higher peak data speeds and more capacity. Sprint's planned use of 8T8R (8 Transmitters 8 Receivers) radios in Sprint Spark also follows the lead of operators in Asia, such as China Mobile, which has used 8T8R with the majority of its TD-LTE base stations.
Sprint is deploying 8T8R to compensate for link budget issues with its Band 41 2.5 GHz spectrum. Using 8T8R results in a "tradeoff in terms of antenna size and antenna complexity," Marquardt observed, but he noted Sprint feels the compromise is worth it to garner extra decibels of link budget for Band 41 spectrum.
"The reason the drive is there for 8T8R is also the reason it is feasible," he added. Higher frequencies such as 2.5 GHz need the decibel gain that 8T8R provides, and, because antennas for higher frequencies are smaller than those for low bands, 8T8R can more easily be used for Band 41 than lower frequencies.
"I don't think you'll ever see 8T8R being feasible at 700 MHz because the antennas are so much bigger to begin with and to have eight of them packaged would be a rather impractical goal from my perspective," Marquardt said.
Sprint CFO: We're banking on 2.5 GHz, 8T8R radios for network differentiation
C-RAN: Plotting next-generation wireless from inside the base station hotel
Sprint details 'America's Newest Network' campaign, focuses on call quality, speeds
Madden: Cloud RAN or small cells?