US wireless operator Sprint demonstrated the first US commercial gigabit LTE network on March 8, 2017 at the Smoothie King Center in New Orleans during an NBA basketball game.  This marks the latest in a series of improvements Sprint has made to its network, and should help the operator gain market share in the US and prepare for 5G.  How gigabit LTE goes for Sprint should also prove informative to China Mobile and other operators around the world that use TDD-LTE spectrum.

In the demonstration, Sprint used Nokia Flexi base stations and a prototype phone model from Motorola.  One phone used alone during the demo attained 706 Mbps downlink (DL) and 8.9 Mbps uplink (UL), between 10 and 20 times faster than a typical connection today, and a whopping 89 times the median 7.9 Mbps seen by users in the US according to Akamai.  Then, Sprint ran three Moto phones at the same time at 300 Mbps each.  Following this, they downloaded streaming HD video to ten devices, a Moto phone and two virtual reality headsets simultaneously without glitches.

The prototype Lenovo Motorola phones used in the demo had a Qualcomm Snapdragon 835 processor and radio chipset with integrated X16 modem:

• DL: The phones used 3xDL carrier aggregation (20 + 20 + 20 = 60 MHz aggregate bandwidth), 256 QAM with up to 4x4 DL MIMO using four base station transmit antennas and four receive antennas in the phones.
• The three LTE component carriers used in the demo phones operate in B41 (2.5 GHz).  Sprint has 160 MHz of bandwidth in B41 in the top 100 regional markets in the US, including Chicago, Dallas, Kansas City and San Francisco.
• Note that the moto phones in the demonstration did not have UL carrier aggregation, which increases UL speed.  See my previous blog on Telstra’s gigabit LTE and the Netgear Nighthawk M1 Gigabit LTE router for more details.

Rumors suggest that the Motorola phones could be prototypes of a new Moto Z model likely to arrive in the second half of 2017.

Sprint uses the industry term Gigabit LTE, but the demo actually fell just short of 1 gigabit per second, which Sprint could attain with a fourth carrier from their 800 MHz, 1900 MHz or 2500 MHz spectrum in properly equipped devices.  Sprint company representatives stressed at the event that the goal of upgrading to gigabit LTE is to increase capacity during peaks hours and in crowded venues like sports arenas, raising speeds for all, not just to increase peak speed theoretically available to a single user.  By increasing network efficiency, capacity and overall speeds, gigabit LTE can make new applications and services practical for consumers, for example those that use virtual reality.

Sprint made early investments in WiMAX for 4G, which put it behind the competition when LTE came along and displaced WiMAX.  After losing cellular subscribers for years and gaining something of an underdog reputation among US operators, in 2014 to 2015 Sprint started investing heavily in its LTE network with the aim of making the best use of its considerable 2.5 GHz spectrum assets.

In late 2015, Sprint launched “LTE Plus,” a faster LTE service that uses beamforming and 8T8R, or eight transmitters and eight receivers per base station sector instead of the more common 2T4R and 4T4R:

• At 2.5 GHz, the wavelength is 12 cm, 25 percent less than at 1.9 GHz, allowing more antennas in the same physical space in beamforming or spatial diversity / MIMO systems.
• LTE Plus increases data rates and capacity, especially for users near the cell edge.
• Launched originally in 70 regional US markets, Sprint has today expanded the service to more than 250 regional US markets.

   

An 8T8R radome and remote radio head for B41.  Source: S4GRU.

Sprint’s Gigabit LTE builds on 8T8R for even higher capacity, faster speed and better user experience:

• In preparation for gigabit LTE, Sprint upgraded its base stations in more than 100 markets to support 3xDL CA in B41 (three component carrier downlink carrier aggregation).
• Nationwide roll-out of gigabit LTE requires Sprint to upgrade from Frame Configuration 1 to Frame Configuration 2, which we presume Sprint can accomplish with a software update to its baseband processors in properly equipped base stations.

Sprint has specified high power user equipment (HPUE) for many of its upcoming phones including gigabit LTE phones:

• HPUE, approved by the 3GPP in December, 2016, raises the maximum allowed transmit power in B41 from 23 dBm to 26 dBm, referred to as Power Class 2.
• The higher transmit power of HPUE improves indoor reception:
  • Under most circumstances, the uplink to the base station has the poorest link budget, and is the first to fail, leading to a dropped call.
  • The downlink, on the other hand, can use spatial diversity or beamforming and the massive radiative power of the base station for a better link budget and better penetration into building structures.
• HPUE has another important benefit to Sprint: it increases the base station cell radius at 2.5 GHz, better matching it to 1.9 GHz.  Most of Sprint’s base stations have radio systems operating at 1.9 GHz and 2.5 GHz located on the same tower.

Many of the premium smartphones selling in the US today support 3xDL CA, including the iPhone 7, Galaxy S7 Edge, and HTC Bolt.  Both the LG G6 and upcoming un-named Motorola smartphone will support 3xDL CA, 4x4 DL MIMO, and HPUE on B41 in versions offered by Sprint.

Sprint’s gigabit LTE is an important step on the way to 5G for Sprint:

• Sprint’s gigabit LTE uses 2.5 GHz spectrum and operates in TDD mode, the same mode as 5G.
• Sprint plans to start rolling out 64T64R base stations later in 2017.  Massive MIMO, defined as MIMO with more than eight antennas, will be another important feature of 5G.
• Sprint is investing in small cells, which 5G will require, and has set up a network with 200 small cells in New York City as a proving ground for high traffic areas.
• So, by upgrading its network for gigabit LTE, Sprint is moving to higher frequencies, TDD, massive MIMO, and densifying its network, all of which should form a good foundation for 5G.

A couple of other observations and comments:

China Mobile has 60 MHz of B41 TDD spectrum, making it a natural candidate for gigabit LTE using 2.5 GHz.  We think China Mobile and other TDD operators can probably learn some things about gigabit LTE base station equipment, smartphones and branding from Sprint’s work on gigabit LTE.  Once China Mobile rolls out gigabit LTE, mobile devices that support it will really hit the mainstream with higher volumes and more choices for consumers, and this will benefit the entire wireless industry.

We tip our hats in recognition of Qualcomm, the first to develop LTE Cat 16 / Cat 13 (DL/UL) processors and radio chipsets, and a big promotor of gigabit LTE.  So far, Qualcomm, Samsung LSI, HiSilicon (Huawei) and Intel have announced LTE Cat 16 / 13 modems for support of gigabit LTE, but only Qualcomm has actually shipped these in production phones and other devices.