Smartphone RF Complexity: Friend or Foe?

Envelope tracking addresses the power challenge of 5G

It’s impossible to escape the attention lavished on 5G at the moment, be it network launches, infrastructure, devices, chipsets, its uses and business cases… the list goes on. However, relatively little is being said about what makes 5G possible and more importantly, how such a power-intensive technology can be made usable in a device as constrained as a smartphone.

About one-third of a device’s battery is used for radio frequency (RF) functions. This is even higher when the screen is switched off, pushing RF to account for the majority of overall power consumption. With every transition to the next generation of cellular technology, power consumption has been a leading challenge alongside increasing complexity in frequency bands. Part of the story is that batteries got bigger, a convenient by-product of the steady growth in the size of displays. But with little progress in improvements to battery technology, this isn’t a solution that scales.

This is why so much attention is being applied to RF front-end technologies from companies such as Broadcom, Qorvo, Qualcomm and Skyworks. They are critical for managing the enormous complexity in the proliferation of spectrum bands and the challenges of interference and power inherent in the system design between the modem and antenna. The advent of 5G significantly increases this complexity with its new spectrum and the introduction of wider channel bandwidths, which have risen from just 20 MHz in LTE to 100 MHz in 5G.

A key technology in this equation is envelope tracking. An envelope tracker actively manages and regulates the power that is applied to the power amplifier in order to minimize power consumption. Although introduced some years ago, it is now becoming a necessity in current smartphone designs given the increased power requirement of 5G radios. It’s a by-product of the additional power needed to deliver performance over high-band spectrum coupled with wider channel bandwidths.

With some carriers also now using high-power user equipment for their LTE and sub-6 GHz 5G networks, the legacy approach of average power tracking is becoming increasingly exposed as devices cannot dynamically adjust the power supplied to the power amplifier based on the input signal from the network. This results in significant battery drain. Indeed, the advantage of envelope tracking increases at higher transmission levels and wider channel bandwidths.

Qualcomm claims that its envelope tracker provides up to twice the efficiency compared with average power tracking at 100 MHz bandwidth. This could mean that phones without 100 MHz envelope tracking have noticeably inferior battery life. This is something we’ll be watching closely as devices based on alternative chipsets from MediaTek and others come to market.

In high-power user equipment mode, handsets can transmit at twice the power from the device to the cell site. Coverage is defined by the link budget of the uplink — that is, the devices the cell site can “hear”. This results in better coverage and consistency in throughput, which delivers greater network efficiency as users can get on and off the network that much faster.

Envelope tracking is just one part of the puzzle when it comes to RF front-end technologies, but it’s a critically important element that affects performance for everyone on the network as well as an individual’s experience. Qualcomm stated in January that almost all the 30-plus 5G devices due to launch in 2019 using its Snapdragon 855 platform and 5G modems will include its RF front-end technologies.

This is indicative of the increased importance of RF technologies to device and network performance and raises the stakes for other suppliers like MediaTek reliant on partners such as Skyworks and Qorvo to deliver solutions. Indeed, the prominent marketing by Skyworks and Qorvo of their envelope tracking solutions is further validation of the importance of the technology.

Qualcomm’s investment in the RF360 joint venture with TDK is looking like a shrewd bet. As ever in mobile chipsets, complexity is the friend of those who can address it, but can also widen the competitive gulf between rivals. With 5G just getting started, it’ll be fascinating to see how the next 12 months plays out.

A version of this article was first published by FierceWireless on 10 July 2019.