Meet the Inventor behind Qualcomm Smart Transmit — a breakthrough technology that optimizes uplink speed and coverage for 5G

Welcome to Qualcomm Invents. In this series, we’re talking with some of Qualcomm’s most prolific inventors about their work, the impact of their inventions, and their inspiration.

Today’s smartphones contain multiple transmitting radios using different technologies — from 2G to 5G, Wi-Fi, & Bluetooth – and antennas covering multiple frequency bands. Optimizing the usage of these radios requires deep understanding across the complex RF system within a phone – and that’s where Qualcomm Technologies’ Lin Lu (VP, Technology) comes in. Her pioneering work in a technology called Qualcomm Smart Transmit uses advanced techniques to intelligently manage transmit power across multiple antenna groups, enabling significantly extended coverage, improved uplink speeds, and lower latency — especially important to meet the high expectations for today’s 5G devices and networks, all while ensuring devices remain compliant with regulatory requirements.

We recently caught up with Lin to talk about the inspiration behind Smart Transmit and her biggest innovations as a principal engineering team leader.

The following conversation has been lightly edited for clarity and length.

Much of your work focuses on electromagnetic interference (EMI) and radio frequency (RF) transmission. How did you end up specializing in these areas?

I started with Qualcomm as a regulatory engineer in 1996. I worked in the commercial base station division and later transferred to the handset division to work on designs to ensure that the commercial devices Qualcomm was developing were in compliance with all EMI/EMC regulations. Our team’s focus was on commercial products.

In 2006, I began working with OEMs to ensure their end products met regulatory requirements. Then, Qualcomm expanded into new technologies, such as wireless charging systems for mobile devices and vehicles. That required us to develop new methodology to assess EMI and RF exposure from these wireless charging systems, because the existing certification test procedure was not yet defined.

Around 2010, when 5G was being scoped out, we identified a significant challenge for 5G commercialization to meet existing regulatory requirements while delivering the increased performance levels promised by 5G — that is, the existing RF exposure assessment procedure would present a roadblock to new 5G technology. The traditional assessment procedure was based on a decades-old assumption that the user equipment (UE, an industry term for devices like phones) would transmit at a maximum power level all the time. The traditional procedure with this maximum power assumption had been used for more than 30 years. However, the UE transmitting power in most transmission events doesn’t come close to maximum power and is inherently “bursty” – meaning that the phone is not transmitting all the time. This legacy assessment approach was therefore overly conservative. We realized this would become a roadblock for 5G commercial deployment, especially in simultaneous transmission scenarios using multiple antennas in the same device.

So, this motivated and inspired me to develop a specialty solution for RF exposure management through novel techniques — so that’s why I focus on this unique area at Qualcomm.

How would you explain EMI and RF exposure limits to someone with limited technical expertise?

That's easy and not easy. EMI, basically, is the need to address interference among equipment or devices. Take your cell phone, for example. You don't want interference with other equipment like your TV. If you turn the TV on and the quality of your phone conversation suddenly deteriorates, that could be caused by interference from other electronic equipment and devices. With RF exposure regulatory limits, the goal is to figure out how much radio energy a device can safely emit — the RF exposure regulations define the allowable energy for uplink transmission, which ultimately defines the performance of a wireless device. Optimizing the RF output helps to improve things like uplink throughput, latency, and coverage, helping to make sure calls don’t drop, videos download smoothly, etc.

Editor’s note: EMI and RF exposure limits are mandatory requirements, regulated by every market in the world, including the Federal Communications Commission (FCC) of the United States.

What discoveries enabled you to foresee transmit power limitations more than half a decade before the launch of the millimeter-wave flavor of 5G, and how did those discoveries eventually impact the development of 5G mmWave technology?

So, the traditional approach — one that was in place since the 1990s — assumed maximum power transmission 100 percent of the time. That's what set a static cap to the power. However, 5G is very dynamic, which means the uplink duty cycle, by definition, can change from a small percent up to 100 percent, and the operating frequency range covers Sub-6 all the way to mmWave.

If we assume a worst-case scenario all the time, then the performance claims expected from a 5G network will never be realized due to this old approach to RF exposure management by statically capping the uplink transmit power. Clearly, we needed a breakthrough.

What we discovered was that the transmitted power and majority of transmissions in the bands are often nowhere close to this maximum power. Therefore, we knew we should be able to support high-power data bursts as needed. My idea then was to optimize UL performance in real time by banking the energy during low-use periods and using it when there’s demand for high power data traffic – such as when inside a building and performing a video or picture upload. This lets the device ensure that the average transmission power in a certain time window doesn’t go over the allowable energy limit. Kind of like a runner jogging most of the time during a race, then sprinting for short bursts when she needs to, but the average speed is constant. This allowed us to maximize the uplink throughput — and unlock the full potential of 5G.

Can you explain how this tech improves uplink speeds and expands coverage? And why it’s so important that the antennas in today’s mobile devices comply with RF transmit power limits?

It's very important because, as I mentioned earlier, this is a mandatory requirement. Without compliance, no one could launch a product, so that's number one. These issues must be resolved in all devices before they go to the market. It’s a must.

Now, how does this technology expand coverage and make 5G possible? Smart Transmit technology lets us optimize radio transmissions dynamically, so that during a time when a stronger uplink connection is needed, we can access it, and most of the time when it isn’t, we can save that energy across the given time window. This allows for more reliable connections, fewer dropped calls, etc.

This seems like a very hands-on testing-intensive area of engineering in the field of mobile technology — can you tell us how you go about developing ideas like this? Is it based in innovation, a focus on regulation, or a bit of both?

I would say it's both. Engineers come up with ideas to solve problems. In my case, once we have this, we then need to define the certification process through development of new test procedures, and test cases. First, because we’re developing new technology. Second, because any commercial device must demonstrate compliance before launching to market.

Once we have the technology we believe will work, we must pivot to make sure it’s in compliance with existing regulations. From there, we must develop certification procedures and test cases — and then we must engage with each regulator around the world to prove we’ve done extensive due diligence and show them that our new idea works. In parallel, we must work with other industry stakeholders such as standards groups and commercial test equipment vendors around the world to standardize the new test procedures and test cases for everyone else to follow.

So, we have this invention, we get to develop the technology, and once we’re there, on the regulatory side, we must do all the other work to ensure the technology is accepted and can be commercialized by our partners worldwide.

How has Qualcomm supported you in your efforts as an inventor? How would you describe the culture of innovation at Qualcomm more broadly?

I spoke earlier about turning an invention into reality, and how it requires a multi-functional team effort. In our case, you can see that from proof-of-concept, to implementation, to regulatory adoption, and all the way through to commercialization. We get support from all around the company — not only from the regulatory team, but the system engineers, software engineers, product management, various local and regional teams, the customer engineering team, test engineers, everybody. This is really needed, and we get support from the entire company. I like to view our successes as a success in team effort. Qualcomm is a company that encourages us all to come up with new ideas and provides all kinds of freedom and support.

Finally, what advice would you give to other inventors?

There are three pieces of advice, based on my experience: enjoy what you do, be persistent, and be cooperative. Enjoying what you do naturally leads to motivation and creativity. Then, being persistent helps you take a good idea and turn it into a reality. And finally, being cooperative is important because every big innovation requires a multi-team effort. My team wouldn’t be where we are today without the support of many other teams.

Read more about other inventors at Qualcomm:

Qualcomm Smart Transmit is a product of Qualcomm Technologies, Inc. and/or its subsidiaries.