Sprint pushes HPUE standard and claims 30% boost in TD-LTE coverage

Sprint has always been first in line to deploy advanced network technologies, even if its efforts have not always resulted in the user experience it was seeking. Its latest effort to end a long period of dissatisfied customers and under-delivering networks comes with its early deployment of HPE (High Performance User Equipment), which it demonstrated in New York City just a week after it was ratified by the 3GPP.

Günther Ottendorfer, Sprint’s COO of technology, said at the event that many device makers were committed to support the standard, though the demo was only able to use prototypes. However, provided the standard does indeed get activated in high profile smartphones, it promises to make Sprint’s key asset, its plentiful 2.5 GHz spectrum, more usable, increasing coverage by 30%, even indoors.

While unpaired (TDD) 2.5 GHz (Band 41) is a strong band for high capacity – and that will be increasingly vital to the 4G user experience and operator business model – it has range limitations, but its uplink coverage will be greatly improved by implementing HPUE, said Ottendorfer.

Sprint has led the development of HPUE, starting work on it in mid-2015 and submitting it to 3GPP with support from a range of other companies. CTO John Saw wrote in a company blog post: “We began working on a solution to improve our 2.5 GHz coverage by increasing the uplink coverage of Band 41 devices. We worked closely with the Global TDD LTE Initiative (GTI) and companies such as China Mobile, SoftBank, Qualcomm Technologies, Samsung, ZTE, Broadcom, MediaTek, Skyworks Solutions, Alcatel, Motorola, LG, Qorvo and others to address the required building blocks. Finally, our team, together with industry colleagues, ushered HPUE through the standards process, and 3GPP certification was granted on December 6, 2016.

HPUE is a handset-based technology which, according to Saw, finally allows Sprint to maximize the benefits of its spectrum in terms of coverage as well as capacity, effectively allowing a higher band like 2.5 GHz to mimic mid-band spectrum like AWS or 1.8 GHz – usually considered the gold standard for a balanced LTE roll-out. “It’s rare to get the best of both worlds,” Saw said.

Sprint claims that HPUE allows its 2.5 GHz coverage strength to become nearly identical to its 1.9 GHz coverage outdoors. Indoors, the technology enables 2.5 GHz to achieve 90% of the in-building penetration that is currently achieved in 1.9 GHz.

The carrier is now working with device providers to build that all-important handset ecosystem and so encourage other operators round the world to support the new standard and harness unpaired 2.5 GHz spectrum. Many operators hold these airwaves, though in some parts of the world it is still mainly used for fixed wireless. However, Sprint parent Softbank and carriers in China and India are using or trialling in the band. A good range of supporting devices will be essential. Sprint expects the first handsets to appear in 2017 – they will need new software, power amplifiers and filters to benefit from HPUE.

Analysts at Jefferies wrote in a client note that HPUE would represent “an important equalizer in our view”.  Sprint has been aggressive this year about boasting of its 2.5 GHz advantage, with which it justified its decision to stay out of the 600 MHz auction – a good call, as it turns out, given the shift of the market towards capacity-driven issues. It has also said that the quantity of its 2.5 GHz airwaves means it “effectively has 5G spectrum” even ahead of any new allocations, and for this reason it has been less interested in early trials in 28 GHz or other high bands, so far at least.

Ottendorfer said Sprint had now moved the majority of its traffic from 1.9 GHz to 2.5 GHz. It has covered more than 300m POPs with LTE, and 75% of those are covered with 2.5 GHz. Its ‘LTE Plus’ service is now available in more than 250 markets (this is Sprint’s brand name for its new generation network upgrade, incorporating LTE-Advanced capabilities such as carrier aggregation and beamforming).

Another key advantage of having over 110 MHz of 2.5 GHz spectrum in most markets is that Sprint has the wherewithal to densify its network considerably using small cells. Ottendorfer said it has deployed 200 small cells in New York City, one of the world’s most challenging RG environments, and seen “remarkable” increase in real word speeds, partly because it can use dedicated spectrum to avoid interference with the macro network.

This is the sort of advantage which Sprint has talked up since the WiMAX days to justify its reliance on 2.5 GHz and its acquisition of Clearwire, the other major holder of this spectrum in the US. Other MNOs will not have the resource to densify at the same rate as Sprint, and in dedicated airwaves, at least until the 5G/millimetre wave stage. But Sprint has, so many times before, thrown away a clear network advantage by failing to commercialize the capabilities effectively, or to support a strong user experience on top of the technology. The jury remains out on whether it will finally create a mobile broadband network which can give it significant competitive advantage over its rivals, rather than just impressing the technology boffins.

Sprint remains a company which loves technology more than real world experience. Its ill-fated Network Vision initiative envisaged a platform of huge ambition, both in technology (density, multiband aggregation and advanced antennas coming into play before they became mainstream tools); and business model (acting as a host for third party networks, an innovative plan which foundered along with initial customer LightSquared). It was replaced last year by Next Generation Network, a simplified approach but with an acceleration of the densification strategy which most effectively harnesses that 2.5 GHz spectrum

According to analyst Jennifer Fritzche at Wells Fargo Securities, in a recent client note. Sprint is finally in a position to practice what it preaches, after spending less than investors expected on its network throughout 2016.

“At Sprint, the carrier has delayed some capex in fiscal year 2016 due to the procurement of permits for its densification plans, so we expect fiscal year 2017 to increase from the $3bn or so it will spend in fiscal year 2016,” Fritzche wrote. “Given the fact Sprint’s liquidity position has significantly improved, we would not be surprised to see this ramp to $5bn-plus. The key question for us (is) if Sprint can achieve such network improvement as it did in 2016 with low spending, what kind of advantage will they get when the real spending starts?”

Sprint is now emphasizing the technologies which will support its belated plan to exploit its 2.5 GHz spectrum sufficiently effectively to leapfrog its competitors in capacity and service quality. In New York, Saw discussed the introduction of three-carrier aggregation, which bonds three separate 2.5 GHz channels to create a single 60 MHz channel.

This hit peak speeds of 225Mbps in a demonstration using an iPhone 7+ (with a custom software upgrade). Customers will see 3CA speeds from early 2017, if they have the right device – initially not an iPhone, but the HTC Bolt, will support the feature on the Sprint network, though Apple and Samsung models can achieve this with a software upgrade.

The operator’s VP of devices told LightReading that 3CA software updates will be available for Apple, Samsung and many other vendors “well ahead” of Mobile World Congress in late February 2017. “By the end of 2017 we’re forecasting that over half of Sprint customers will have … compatible phones,” he said.

Saw added that Sprint had “already started working on five-channel CA, which is what you need for 5G … a 100 MHz channel.” These very wide channels have mainly been discussed in terms of 5G in high frequency spectrum, though Sprint itself has been less preoccupied by bands like 28 GHz, claiming its 2.5 GHz mountain will suffice for some years, even for 5G migration.

And  Saw demonstrated a prototype antenna array with 128 tiny elements, designed for high frequency bands. The Massive MIMO array, from Nokia, is beginning tests with Sprint this month and though Saw gave no timescales for live deployment, he echoed other operators in saying that these antennas would help deliver gigabit ‘5G’ speeds on current spectrum, and before the operator needs to migrate to a new 5G radio.

Sprint currently uses eight-transmitter, eight-receiver (8T8R) antennas in its 2.5GHz network while the new models would boost that to 64T64R, a technology which can only work in higher frequencies because of antenna size and limited bandwidth lower down the spectrum.

This is one of the reasons why Sprint shunned the 600 MHz auction (and the bidding has proved far less eager than expected). Carriers’ priorities are shifting to the speeds and data capacity which can only be achieved with higher band spectrum, and targeted zones of dense small cells.

At a recent investor conference, Sprint CFO Tarek Robbiati said the 600 MHz band was the “spectrum of the past”, adding: “We did not participate in the 600 MHz auction not because we didn’t have money at the time, or we were under-resourced for it. It is simply spectrum that is spectrum of the past. The world is moving toward high capacity wireless data networks, and in that world the best and most efficient spectrum that is needed for that… is mid-band spectrum, the spectrum that we have, the 2.5 GHz spectrum.”

That is demonstrable in developed mobile markets. Now Sprint just has to prove that, this time around, it can actually harness its huge but under-exploited 2.5 GHz spectrum asset, to outdo its rivals’ own densification and pre-5G initiatives before the next generation of networks arrives.

“Everything we do is a lead up to this 5G world,” Ottendorfer concluded.