AT&T needs unlicensed spectrum to reach 1 Gbps on LTE, but T-Mobile doesn’t

AT&T will make use of a variety of technologies to boost its LTE network speeds to 1 Gbps, including unlicensed spectrum.

AT&T’s top network executive said the carrier will rely in part on unlicensed spectrum in order to raise the speeds on its LTE network to 1 Gbps. However, a top T-Mobile executive said the carrier wouldn’t necessarily need to use unlicensed spectrum to reach those speeds on its own LTE network and would instead rely on its licensed spectrum holdings.

AT&T’s John Donovan said that the carrier would make use of a variety of technologies to boost its LTE network speeds to 1 Gbps, including 4x4 and 8x8 MIMO, 256-QAM and carrier aggregation. He also said that AT&T would need to use unlicensed spectrum to reach those speeds and mentioned Licensed Assisted Access (LAA) as a technology that the carrier could leverage. LAA essentially allows wireless network operators to transmit LTE signals in unlicensed spectrum bands, like those used by Wi-Fi networks.

Going to unlicensed bands “allows you to have a much broader swath of spectrum,” said Donovan, chief strategy officer and group president of AT&T’s technology and operations.

But T-Mobile’s Karri Kuoppamaki said the operator will not need to rely on unlicensed spectrum bands in order to reach 1 Gbps speeds on its LTE network.

Indeed, during T-Mobile’s uncarrier event last week, CTO Neville Ray explained how the carrier might reach those speeds. “How do you get to gigabit LTE, how do you do 60 MHz? So here’s the math: 5 megahertz carrier gives you about 35, 38 megabits per second. 256 QAM takes it to 50, 4x4 MIMO takes it to 100 MIPS. Ten of those gives you a gigabit,” Ray said during the event. “So you actually don’t need 60 megahertz, … you only need 50 megahertz. You can look at our spectrum holdings; there are places in the country where we can get to that on a downlink.”

But Ray added that T-Mobile too continues to look at unlicensed spectrum and LAA technology to increase its network speeds: “We’ve been the primary driver of using unlicensed LTE, which makes speeds in excess of a gigabit per second even feasible.”

Arun Bansal, head of business unit network products, explained that 1 Gbps speeds on LTE are partly dependent on operators’ spectrum holdings: “It depends on the spectrum availability for operators.”

Indeed, Ericsson participated in T-Mobile’s recent tests on the topic. The companies said they achieved peaks of 979 Mbps, with stable throughputs well above 900 Mbps, in an over-the-air demonstration of LTE. The companies said the demo took place in T-Mobile's lab in Bellevue, Washington, and used 60 MHz of total carrier bandwidth alongside 3CC carrier aggregation, 4x4 MIMO and 256 QAM functionality on the downlink.

But Bansal cautioned that actual users should not expect real-world 1 Gbps speeds on LTE. “When we say 1 Gbps, it means one cell, one radio will deliver 1 Gbps. That does not mean that every user will get 1 Gbps. It means you can have more number of subscribers in a given area having a reasonably good experience.”

AT&T and T-Mobile are among the U.S. carriers racing to reach the 1 Gbps milestone on LTE ahead of the industry-wide move toward 5G technology. Indeed, Sprint, T-Mobile and AT&T have each promised to offer 1 Gbps services on LTE in the future.

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