Qualcomm — the premier provider of advanced mobile communications technology — and T-Mobile — the “un-carrier” carrier that pushed the industry toward unlimited data plans in the United States — threw a press and analyst event in San Jose last week that represented a coming out of sorts for gigabit LTE, the new high-speed version of 4G technology already in place throughout most of the developed world.
Although the name implies data rates of one gigabit per second, an individual will rarely achieve this theoretical maximum. After speechifying for a bit, the two companies showed various live demos that saw peak rates in the 600Mbps range, but they had made some attempt to simulate real conditions by loading the network with lots of devices at the same time, half of them gigabit-enabled, and half from the prior generation.
At three demo stations, the teams illustrated a virtual reality application with goggles, a large photo directory copying operation, and a pretty sizable video download. Each station compared the new handsets to the old ones, and they ran them all at the same time to load up the network, which was a local femto cell set up in the demo room.
In all cases, the new phones completed their tasks by double-digit percentages faster than the old ones, but one slightly surprising and counterintuitive result was that the old phones’ performance improved markedly once the new ones were done and off the network.
One analyst cracked that this amounted to altruism, and that he intended to buy one for himself, telling his wife, “I’m doing it for you, honey.” That the performance of her old phone would be improved by his getting himself a new one would amount to an act of charity. We speculated about whether he could take a tax deduction for it.
What made it a coming out party? The technology has been around for about a year, with its first introduction in Australia by Telstra, the one of the national carriers there. But the T-Mobile announcement marked the first major rollout of gigabit LTE in the United States, lighting up 430 cities out of T-Mobile’s 920 already enabled with LTE-Advanced, the next-most-recent standard.
What made it possible for T-Mobile to do such a rapid upgrade — putting aside for a moment the billions invested on spectrum and hardware since 2013 to complete LTE (4G) coverage — was that the hardware upgrade for gigabit LTE is entirely on the handset side. Once a firmware upgrade is transmitted to the base stations, the network is ready to accommodate the new phones.
Specifically, the base stations already have four antennas per channel. The new phones bring the device side up from two to four, enabling 4x4 multiple-input multiple output (MIMO) radios, a key pillar of gigabit LTE.
The other two pillars are 256 quadrature amplitude modulation (QAM) and carrier aggregation across three bands, which together with 4x4 MIMO wring the extra performance out of existing LTE networks to get to the gigabit level.
A bit about QAM. Information is transmitted through the air via radio waves, and these waves have a cycle, some number of cycles per second. In the old days, data rates were limited by this speed. You couldn’t encode any more than one thing per cycle. But some clever people figured out that you could shift the signal in two dimensions, phase and amplitude. Phase shifting was back and forth in time. Amplitude shifting was essentially volume adjustment. So, first by creating 16 possible states out of four phases and four amplitudes, every cycle could transmit four bits at once. A 2400 baud modem became a 9600 bit-per-second modem. In 256 QAM, the technology has been refined to be able to distinguish 16 different phases and amplitudes, yielding 256 possible states of 16 bits. So, now each cycle can be encoded with 16 bits.
Carrier aggregation is really just using multiple bands at the same time. A carrier band is often 20MHz wide. The higher up the spectrum it is, the more cycles per second are there to be encoded. But by grabbing a couple of bands — or in the case of gigabit LTE, three — and making sure to keep the order of all the data sent by each of them straight, the new technology can triple the data rate of a single carrier.
There are lots of tricks with the antennas, but essentially, by having four on both ends — the base station and the device — they can interchange that much more data.
Qualcomm’s vice president of marketing, Pete Lancia, took pains to point out that gigabit LTE is “beyond theory.” He cited 43 operators in 25 countries with 16 devices (most of them phones) as evidence that gigabit LTE is more than just a pilot now.
Both Mark McDiarmid, vice president of network engineering at T-Mobile, and Lancia cautioned against mistaking gigabit LTE for 5G, the next big standard, with McDiarmid promising, “We’re not going to call gigabit LTE 5G,” and Lancia christening gigabit LTE “the foundation for 5G.”
Still, gigabit LTE will make an immediate difference in the way mobile communications users perceive network responsiveness, letting them do things in new ways that weren’t possible before, like not having to decide what video to choose the night before a trip, knowing they can download a full movie in a few seconds just before boarding the plane.