Wideband LTE’s Time is Now as Carrier Aggregation Waits in the Wings

Thu, 07/31/2014 - 3:36pm
Ben Munson

T-Mobile calls it Wideband LTE. Verizon calls it XLTE. Branding changes but the offering is similar. Those carriers are referring to LTE deployments of 15x15 MHz or more.

T-Mobile has been hard at work acquiring AWS spectrum in order to reach its goal of covering 90 percent of the top 25 markets with 20x20 MHz LTE. Verizon, flush with AWS from auctions and a 20 MHz nationwide swath it bought in 2012 for $3.9 billion, is deploying 30 MHz and sometimes 40 MHz chunks of spectrum on top of the 10x10 MHz it used for its 700 MHz LTE network.

Both carriers own large contiguous blocks, making it easier to combine the channels. Well, easier than using carrier aggregation.

“If you have contiguous 20 MHz spectrum, you’re probably not going to be doing carrier aggregation to get to 20 MHz,” said Peter Jarich, an analyst with Current Analysis.

Carrier aggregation is only one component of the emerging LTE-Advanced feature set but it’s received the most attention so far. Maybe that’s because it’s more fun to say than Relay Nodes but more likely it’s because of the phone-melting downlink speeds it’s capable of producing. South Korea’s SK Telecom earlier this year successfully stitched together three LTE bands (one 20 MHz and two 10 MHz) and was able to support speeds up to 300 Mbps.

But those blazing fast speeds only come after clearing some significant technical hurdles to bring non-contiguous spectrum—within the same band or from separate bands—together to form a large carrier.

“[Carrier aggregation] is a more complex deployment due to the additional configuration parameters,” Yankee Group analyst Ken Rehbehn said. “Plus, if the aggregation is between low and high bands the complexity grows as the operator must fret over power levels.”

If a carrier, like T-Mobile, has enough headroom to provision a larger channel size, they’ll do it, Rehbehn said. If the carrier, like AT&T, doesn’t have enough contiguous spectrum, carrier aggregation may be the best option.

But the FCC’s fast-approaching AWS-3 auction should change the outlook. The Commission intends to raise more than $10.5 billion by auctioning off 65 MHz. A 1695-1710 MHz band of unpaired spectrum will be sold for uplink. The 1755-1780 and 2155-2180 bands will be paired and sold as three 5x5 MHz blocks and one 10x10 MHz block.

The AWS spectrum the FCC is putting up for grabs should be particularly enticing to AT&T. When the carrier acquired Leap Wireless, it got 23 MHz of spectrum in markets like Washington, Philadelphia, Denver, Houston, San Antonio, San Diego and Portland that sits near the AWS licenses up for auction. So savvy bidding this fall could set AT&T up for a wideband LTE offering of its own.

As AT&T and other potential bidders await the AWS auction, AT&T is nearing the end of 2014, when it previously said customers could start seeing faster downlink speeds from aggregating the 700 MHz unpaired spectrum the carrier bought from Qualcomm. The carrier calls its supplemental downlink.

As AT&T moves forward with its carrier aggregation plans, Verizon and Sprint have also promised to put the technology to work soon. Even T-Mobile, with its healthy contiguous spectrum holdings, has said it will leverage aspects of LTE-Advanced at some point.

Given the mind-boggling speeds carrier aggregation could make possible through the theoretical combination of five 20 MHz channels into one 100 MHz super pipe, it’s hard to not be interested.

“I do think you’ll see [carrier aggregation] in the U.S. It’ll be important,” Jarich said.

But for now it’s contiguous wideband LTE that’s putting up the peak speeds, while carrier aggregation awaits its chance at breaking those speed limits.



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