Three well-known technologies come together. Gig LTE isn't magic, just darn good engineering. More spectrum is put to use through carrier aggregation. Early LTE used a single 20 MHz band. Gig LTE will use three or four bands. More antennas send more signals, usually four. (4x4 MIMO). Advanced modulation (256 QAM) carries 8 bits per signal rather than the 6 bits of the earlier 64 QAM, a third more. All three were added to the LTE specs between 2009 and 2012, but only now are improved chips and radio frequency components in mass production.
More spectrum. Early 4G LTE used 20 MHz spectrum bands and achieved up to 150 megabits.
Combine two, three, four, or five 20 MHz bands and speeds go up proportionately. In 2016, three carrier aggregation - 60 MHz - is becoming available from T-Mobile in much of the U.S., SK in Korea, and some others. I don't believe anyone is actively supporting 4 carriers, or 80 MHz, which is expected to become common in gigabit LTE. At maximum, 3 carriers can deliver 3 times as much as the single carrier, 450 megabits. In Swisscom testing, below, the three carriers reached 338 megabits, a more realistic figure. The more spectrum, the more calculations the phone must do and the more radio frequency filters in the analog front end. The problem is compounded because the spectrum bands are scattered and different for each carrier and each country. Sprint, for example, has spectrum at 800 MHz, 1.9 GHz, and 2.6 GHz. AT&T has some at 700 MHz, 1800 MHz, and 2300 MHz. To be able to serve most companies around the world, the iPhone 7 covers 24 bands just for LTE. Even with remarkable advances in radio frequency front end components, working with so many bands adds considerable cost and complexity.
The engineers developed practical ways to join bands for high speeds around 2013. It wasn't easy and I don't recall any three band deployments before 2016. LTE is defined as up to five bands - 100 MHz - since 2009, so there's still room to grow. More recent standards go even higher. 5G millimeter wave will use several hundred MHz or even a GHz, 1000 megahertz. The complexity and power demands go up as well. Top analyst Linley Gwennap expects early mmWave chips to be 10X as complicated as today's state of the art and real battery killers. It will take at least another generation of Moore's Law and probably two generations before mmWave phone processors will match the power and size of today's LTE chips. That's one of the reasons it will be at least 2020 and probably 2022-2024 before mmWave phones become common.
More antennas. Arogyaswami Paulraj in 1993 discovered that you can derive separate signals from two transmitters, even if they are very close. The signals bounce off walls and other obstacles slightly differently and a good receiver can tell them apart. (If you have perfect line of sight, MIMO does very little to improve performance because it doesn't get those bounces.) Wi-Fi 802.11ac has used four antennas for several years, but it's only now four antenna cell phones are becoming available.
256 QAM carries eight bit per signal. It's more sensitive to noise but today's components reduce noise considerably.
Put these three together and you can get over a gigabit (shared) if you have a good connection. Push a little further, including to five bands, and you get almost two gigs. Huawei and BT did a demo of 2 gig LTE, but production gear is unlikely before 2018 or 2019.
For the record: I'm not an engineer by training, but I've learned this from some very good engineers.
Ericsson and Swisscom Achieve new world First in LTE-Advanced
- Technology leaders Ericsson and Swisscom demonstrate 256 QAM in a combined three-carrier aggregation LTE FDD/TDD live commercial network
- New 256 QAM modulation scheme enhances the data rate of existing frequency spectrum by up to 30 percent
Ericsson (NASDAQ: ERIC) and Swiss operator Swisscom have on September 17th, 2015 achieved another LTE-Advanced world-first in a live demonstration in Swisscom’s commercial mobile network.
By introducing 256 QAM (quadrature amplitude modulation) in a combined three-carrier aggregation LTE FDD/TDD network, the partners achieved peak downlink speeds of over 426 Mbps, compared with 335 Mbps recently achieved with the same set-up in Swisscom’s commercial network with current 64 QAM technology for downlink.
Ericsson and Swisscom have previously demonstrated Europe's first fully commercial LTE-Advanced three-carrier aggregation solution combining LTE in both FDD and TDD modes.
Patrick Weibel, Senior Architect Wireless Strategy, Swisscom, says: “At Swisscom, it is always our ambition to innovate to offer our customers the best network at all times. 256 QAM will add an important feature to the modernization of our LTE-Advanced network by increasing data speeds up to 30 percent without using any additional spectrum.”
For the demonstration, held in Zurich, Switzerland, 256 QAM was introduced using software from the recently announced Ericsson Networks Software 16A, which will become commercially available later in 2015. The three-carrier aggregation solution in Swisscom’s live commercial network makes use of two LTE TDD carriers, each with 20MHz bandwidth in the 2.6 GHz frequency band (B41), and one LTE FDD carrier with 15 MHz in the 2.1 GHz band (B1).
Per Narvinger, Head of LTE, Ericsson, says: “Ericsson Networks Software 16A introduces numerous features that help operators take important steps towards improved app coverage in the Networked Society. One of these features, 256 QAM modulation, significantly improves data throughput in any given LTE spectrum. We are proud to provide our partner Swisscom with another world-first innovation.”
About carrier aggregation and 256 QAM:
Carrier aggregation and 256 QAM are two features of LTE-Advanced. With carrier aggregation, several carriers in non-contiguous frequency bands can be combined and treated as one. The current Ericsson Networks Software 15B can achieve up to 450Mbps in downlink by combining three 20MHz carriers in LTE. 256 QAM, part of the new Ericsson Networks Software 16A, improves the data throughput in a given spectrum by up to 30 percent, meaning that a three-carrier LTE-Advanced network can achieve up to 600 Mbps downlink.
From T-Mobile's Neville Ray. There's some bluster and competitor bashing, but his description of how these features work is on target.