CHICAGO -- Light Reading's Big Telecom Event 2014 -- Sprint sparked up the morning keynote of Light Reading's largest-ever event with a tale of how it will up its LTE speeds in US cities through 2015.

Jay Bluhm, vice president of network development and engineering for Sprint Corp. (NYSE: S), kicked off Day 2 of BTE with a rundown of the carrier's ongoing 3G and 4G updates with Network Vision and Spark. Bonding radio channels with carrier aggregation through LTE Advanced is at the basis of the Spark update, but Sprint takes it further with software upgrades, multiple antennas (MIMO), and updated radio technology at the cellsite, alongside tri-band MIMO rollouts on the device side.

"By 2015 you're going see these peak speeds of 180 Mbit/s, where you're getting peak speeds of 60 Mbit/s today," Bluhm told the audience. (See Sprint's Spark: It's Fast but No Multi-Tasker.)

Bluhm Sparks Up BTE Sprint's Jay Bluhm talks LTE in Chicago.

At the very heart of the Spark upgrade is 1,900 MHz, 800 MHz, and 2.5 GHz tri-band LTE support: 1,900 MHz is the workhorse frequency that gives Sprint widespread outdoor coverage; 800 MHz provides better indoor coverage and improved range; while the 2.5 GHz channel is the racehorse, providing peak speeds in urban areas. (See Igniting the Future: Sprint Spark.)

Triple Threat Sprint's Workhorse, Pony Express, and Racehorse frequencies for LTE depth.

8T8R? Come again?

Multiple antenna arrays combined with eight-transmit/eight-receive (8T8R) radios at the cellsite will boost the range and speed of the LTE TDD 2.5 GHz element of Sprint's Spark offering. Sprint has said previously that it will start deploying that technology around the middle of this year. (See Defining 4G: What the Heck Is LTE TDD?)

8T8R is a term that we are all likely to see more of soon. Current cellular design typically uses two transmit and receive paths -- 8T8R has eight. 8T8R enables wide-range "beamforming," which means that the operator can direct a beam to a specific user's device, improving the speed, range, and signal-to-noise characteristics of the transmission. (See Sprint: LTE TDD Speed Boost Coming Soon.)

Long-time readers will remember that these concepts were originally tried out with WiFi, way back in 2002. They were also floated as a WiMax booster, but LTE overtook that specification as the preferred 4G technology. (See Vivato Switches Sides.)

8T8R has become possible for cellular because the technology has shrunk enough that a multi-element antenna array and a remote radio head (RRH) can be installed to support 8T8R at a cellsite. For instance, Alcatel-Lucent (NYSE: ALU) writes that its "RRH on band 41 [2.5 GHz] supports up to 160 W total (8 times 20 W) and up to 120 MHz of aggregated carrier bandwidth to fit with Sprint large TDD bandwidth and capacity needs." (See What the [Bleep] Is Fronthaul? for more on what RRHs are.)

Beamforming and vastly increased transmit and receive paths will likely eventually become part of the 5G specification, too. (See DoCoMo Unveils 5G Trial Plans.)

Don't forget that MIMO and multiple frequencies will also require bigger antenna arrays and tri-band support at the device for best performance. Bluhm notes that Sprint already has a raft of tri-band devices available as it deploys Spark upgrades in major US cities. (See Fanning Sprint's Spark in NYC.)

The Big Picture The board tech elements that will allow Sprint's speed bump.

Sprint has access to up to 120 MHz of 2.5 GHz TDD spectrum in 100 major markets, Bluhm says. This means that it is planning to hit three-channel radio carrier aggregation on that frequency in 2015.

Now We're Bonding Three-channel carrier aggregation delights the radio wonks in the crowd in Chicago.

Carrier aggregation in the LTE Advanced specification (3GGP Release 10 and beyond) is at the root of Sprint's Spark advance, Bluhm says, but the operator will take it further with software updates and device support. "The infrastructure we're deploying is capable of supporting three carriers, which will get you 180 Mbit/s peaks."

— Dan Jones, Mobile Editor, Light Reading