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Understanding HPUE

December 20, 2016 | For the last Opinion… of 2016, we are returning to the subject we started with at the beginning of the year – Sprint.  A few days ago, Sprint, along with a host of vendors and partners, announced support for HPUE or High Performance User Equipment.

HPUE applies to Sprint’s 2.5 GHz TDD network and associated spectrum, and the company claims up to 30 percent increase in cell cover from the new technology.  It should be noted that HPUE is a 3GPP standard that applies to the 2.5 GHz TDD band (Band 41) and is also to be used by China Mobile and Softbank.  HPUE was developed as part of the Global TDD LTE Initiative (GTI) which includes Qualcomm Technologies, Samsung, ZTE, Broadcom, MediaTek, Skyworks Solutions, Alcatel, Motorola, LG and Qorvo.

To break this apart and provide an explanation of how it works and the impact, we asked ourselves a few questions and then sought the answers. Here goes.

1. How does HPUE work?

Simple – HPUE increases the transmit power from the device to the cell site (the uplink).  Getting technical for a minute, Sprint and its partners have proposed and gotten approval to increase the transmit power of the device when using Band 41.  Power increases from Power Class 3 (max transmit power of 23 dBm) to Power Class 2 (max transmit power of 26 dBm).  So the HPUE devices use a more powerful radio when using Band 41.  Note that 3GPP has done other work similar to this, notably in the 700 MHz band (Band 14).

2. Why does HPUE increase the cell site coverage area?

As it turns out, the cell site coverage is defined by the link budget of the uplink.  In simple terms, the cell site coverage is defined by the devices the cell site can ‘hear’. Think of this as the cell site having a megaphone and blasting out the signal: it is loud and can be heard over a wide area. The cell site antennas are mounted high up (on a macro cell) and can be ‘heard’ for some distance. But, by comparison, the device radio is small, equivalent to a person shouting without a megaphone. For two-way communication, the cell site needs to be able to hear the device and hence the cell site coverage is limited by the uplink.

Sprint has said that HPUE increases the cell coverage by up to 30 percent.  The impact will also be seen indoors; simply, the cell site will be able to connect with more devices, as their uplink signals will be able to penetrate the building skin.

3. What is the real life impact of this?

Sprint and its partners in the announcement claimed that HPUE makes the 2.5 GHz band ‘nearly’ act like 1.9 GHz spectrum.  Since the ability of a signal to propagate through the air increases as the frequency drops (700 MHz propagates further than 1900 MHz for example), this makes sense.  The 1.9 GHz bands use the lower power class and hence have a weaker uplink; by boosting the uplink of the 2.5 GHz signal, you can get closer to performance parity.

For Sprint, this means that the 2.5 GHz TDD network can increase its effective coverage and more consumers will be able to use a given cell.  The exact impact will, of course, depend on how Sprint’s network is architected in a given area.  There will be no improvement in the signal in other bands Sprint uses.  And Sprint will not be able to extend coverage where the 2.5 GHz cells are not currently located.  

4. Can existing smartphones and devices use HPUE?

Sprint has announced that HPUE devices will be available in the first half of 2017.  Consumers will need a new device; existing smartphones cannot be upgraded since a new chip is required.  Software alone cannot increase the transmit power of a specific band; that needs a new chip.  Note that Qualcomm, Broadcom and MediaTek were both included in the announcement.

The need for new devices means that Sprint will have to wait to get the benefit of HPUE until sufficient devices have penetrated the user base.  Assuming devices are on sale in the first half of 2017, it will likely be a couple of years before the real impact is seen.  Do the math: assume that 40 percent of Sprint subscribers get a new phone every year and sales are split 50/50 between Android and Apple.  If Android devices are available mid-2017 and Apple is available at the end of 2017 (just an assumption), then 10 percent of Sprint’s subscribers will use HPUE by the end of 2017.  By the end of 2018, this figure could be up to 50 percent.

5. What about Apple?

Apple and the iPhone were notable by their absence from the announcement.  But at the media event in New York, Sprint did a demonstration of three-carrier aggregation using an iPhone 7 Plus.  Samsung was included in the announcement and so devices can be expected from the south Korean OEM.  iGR expects others, including Apple, to follow at some point in 2017 given the fact that China Mobile will also be using HPUE in its 2.5 GHz TDD spectrum, and China means a lot of volume for Apple and other devices OEMs.

6. Can HPUE be applied to other bands other than 2.5 GHz?

Yes, but it is not as easy as it sounds.  If the spectrum is ‘clean’ and ‘new’, with no existing devices, then the transmit power can be set by the ecosystem; tests do have to ensure that there is no interference with adjacent bands, so you cannot simply turn up the transmit power to 11.  The problem comes if a spectrum band is also using GSM and UMTS, for example.  In this case, if the LTE device uses Power Class 3 and the GSM/UMTS devices use Power class 2, problems will ensue since the network topology will change.  But for ‘new’ bands such as 700 MHz, which is only used for LTE, the Power Class can be set without worrying about backward compatibility to GSM and UMTS.

There will likely be the same opportunity with 600 MHz once the auctions are finalized.  Since 600 MHz is ‘new’ to mobile devices, once the broadcasters have been relocated, the only devices using 600 MHz will be LTE devices. The Power Class can then be set as needed (pending interference tests).  But remember that 600 MHz signals will go a long way and there is less need to boost the device power.

7. Are changes needed at the 2.5 GHz base station?

No, and this is the cool part: the improvement in coverage comes from simply improving the device uplink power.  So Sprint, China Mobile and Softbank will not have to visit their cell sites to make changes; they just need 2.5 GHz TDD devices with HPUE to get the benefit.

Have a good holiday season and see you in 2017.

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