How mobile phones can save, not waste, energy

The mobile industry is experiencing explosive growth worldwide, fuelled by almost 7 billion subscribers and an ever-growing demand for data traffic. However, the energy efficiency of mobile networks remains extremely low. Both base stations and smartphones regularly waste 70% of the energy consumed as heat. The underlying power architecture used in mobile communications still relies on outdated technology developed during the 1930s.

The impact of relying on such outdated technology is huge. The mobile industry consumes 1% of global power consumption. At first thought, that may not sound like much, but it’s actually more than the power output of all the coal-fired power plants in the United Kingdom, which generate significant greenhouse emissions and contribute to accelerating climate change.

From a financial perspective, mobile operators can spend up to 50% of their operating expenses on utility bills. With $36 billion being spent globally to power mobile networks, this amounts to wasting more than $25 billion annually; money that could be put to better use. It’s also a tremendous challenge to bring the benefits of mobile communications to the 1.7 billion people who live off electricity grids. The substantial power requirements of base stations means that these cannot today be powered by renewable energy alone, so they rely on costly and dirty diesel, despite the associated logistical and security challenges. And, finally, smartphone users experience the frustration of high-power consumption on a daily basis – when their phones run out of battery.

To understand why we have these problems, and what can be done to address them, we need to look at how mobile radio networks are designed. At the core of mobile communications is the use of radio spectrum, a scarce resource that is typically auctioned and licensed by different national governments. Occasionally, new spectrum bands open up, but we are essentially looking at a finite resource. At the core of the challenge is a classic dilemma: ever since the advent of mobile communications, radio engineers have been confronted with a fundamental design choice of optimizing either power efficiency or spectrum utilization. In plain language, this means radio engineers can either design for effective use of the spectrum or for low power consumption, but not for both desirable properties at the same time.

When mobile communications were in their infancy, this dilemma was less significant – mainly because the subscriber base was small and data traffic limited. The 2G protocols (such as GSM and CDMA) used the radio spectrum less efficiently; the result was high levels of power efficiency for voice communications. Think back and you will probably remember the days when you only charged your phone a few times per week, rather than twice a day.

Over time, and as the mobile industry grew, radio engineers have been forced to rethink this initial solution. This has been brought about by the rapid adoption of smartphones, tablet computers and laptops, together with the emergence of cloud-computing applications that require constant network communications. As a result, radio spectrum has become an ever-scarcer resource, which mobile operators need to use as efficiently as possible. Hence, the trade-off between power efficiency and spectral efficiency has swung decidedly in favour of the latter. The unfortunate consequence for many users is that they still need to charge their smartphones twice a day, because the power efficiency has been reduced to accommodate greater spectral efficiency.

The key power-using component in both base stations and smartphones is the power amplifier (PA). While conventional PAs can achieve high levels of efficiency, the problem is that they can only do this at one power level. Advanced wireless standards such as LTE achieve high data rates in part by requiring the PAs to change their output power level over a range exceeding 10:1. High data rates demand that the PA navigate this wide range with extremely high speed and accuracy. These requirements put into play the brutal trade-off so familiar to radio engineers: they must slash PA efficiency to achieve high data rates.

The fundamental reason why smartphone battery life continues to decrease is that the demands of modern data bandwidth have outstripped advancements in PA architectures. The result is a situation where a lot more power is used than is actually needed for the radio signal.

For years, radio engineers have been trying to find a more efficient way of powering the radio signal. Surely, it must be possible to avoid wasting 70% of the energy consumed? Unfortunately, a solution has proven elusive.

There have been modest incremental efficiency improvements to existing power amplifiers, as well as a number of failed attempts to introduce new power-saving technologies. For a long time, the most promising new technology was Envelope Tracking (ET), which fell short of expectations for two reasons. First, the technology only really works for smartphones and not for base stations, which consume the bulk of the power used in mobile communications. Second, while ET works for narrowband communications, the technology falls flat when deployed in the latest generation of wideband networks. This means that ET is a technological dead end, one that can’t resolve the power challenges faced by the mobile-communications industry, either today or in the future.

It is against this background that Eta Devices was established. The company’s patented technology, ETAdvanced, is based on 10 years of research at MIT by electrical engineering professors Joel Dawson and David Perreault, both co-founders of Eta Devices. Dawson and Perreault developed this breakthrough transmitter architecture by combining their expertise in the fields of power electronics and power amplifiers. ETAdvanced works like an automatic gearbox, constantly providing the right amount of power for the radio signal. This has led to an 80% reduction in the amount of heat waste over conventional power amplifiers deployed in today’s base stations.

The result is that mobile operators can now save billions of dollars in utility costs, consumers have smartphones with 50% longer battery life and the industry can cut its annual greenhouse gas emissions by an amount corresponding to nearly 5 million American homes. Given their low energy consumption, mobile base stations can now be powered exclusively with renewable energy.

Author: Mattias Astrom is co-founder and CEO of Eta Devices, a World Economic Forum Technology Pioneer of 2015

Image: Men are silhouetted against a video screen as they pose with smartphones in this photo illustration taken in the central Bosnian town of Zenica, May 17, 2013. REUTERS/Dado Ruvic