David Perez-Lopez, senior research scientist, Nokia Bell Labs. Image: Nokia Bell Labs
David Perez-Lopez, senior research scientist, Nokia Bell Labs. Image: Nokia Bell Labs

Sick of terrible Wi-Fi? There’s a researcher for that

21 Jun 2017

David Perez-Lopez is a senior research scientist at Nokia Bell Labs, working on new technology to improve Wi-Fi.

This week, we’re diving head first into the world of research to uncover what it’s all about.

There are so many spectrums to research, and, as it’s often deep in the back of the lab for months and even years before we hear anything about it out in the real world, it can all seem a bit confusing.

From food and healthcare, to autonomous cars and telecommunications, there are countless researchers working on the newest technologies and innovations to improve our lives.

One such researcher is David Perez-Lopez. Here, he sheds some light on his work at Nokia Bell Labs, and how he hopes to fix our Wi-Fi problems.

What is your role within Nokia Bell Labs?

I am a senior research scientist within the small cell team of the Access Laboratory at Nokia Bell Labs, and my main research focus is on future telecommunication systems – in particular, ultra-dense small-cell networks and multi-antenna technologies.

What education and other positions led you to the role you have now?

Prior to Nokia Bell Labs, I received BSc and MSc degrees in telecommunication from Miguel Hernández University in Spain in 2003 and 2006, respectively, and a PhD degree in wireless networking from the University of Bedfordshire in the UK in 2011.

I was also a radio frequency engineer with Vodafone Spain from 2005 to 2006, and a research associate with King’s College London from 2010 to 2011.

Can you tell us about the research you’re currently working on?

While traditional mobile network operators (MNOs) – which have always run on licensed spectrum to provide quality of service – used to see investing in unlicensed spectrum solutions as a means to feed competing technologies, they now embrace unlicensed spectrum as a tool to efficiently address the exponential growth of traffic demands.

Scarce and costly licensed bands can be relieved by offloading best-effort traffic to unlicensed ones. Conversely, licensed technologies can take over when unlicensed ones happen to fail, thus providing enhanced quality of experience and reliability.

This allows them to promptly deal with reduced coverage, increased interference, or even a radar operating in the same band. Better still, with a licensed-plus-unlicensed heterogeneous spectrum, MNOs can seamlessly offer larger bandwidths, and thus improved performance to their end users, eg, in terms of higher data rates.

However, the provisioning of quality of service in unlicensed spectrum is challenging, as multiple service providers using different technologies – cellular, Wi-Fi, Bluetooth – can co-exist in the same band, and a good inter-operator and inter-technology coordination in a decentralised manner is hard to achieve.

As a matter of fact, current coordination is quite simple and based on listen-before-talk, a procedure by which a node attempting to use an unlicensed channel must assess whether the channel is busy or not before transmission, and then decide accordingly whether to transmit or not. This results in poor spectrum usage when the number of nodes trying to access the band is large, as the probability of collision (two nodes accessing the medium simultaneously) is high.

Currently, I am working on massive MIMO [multiple input, multiple output] unlicensed (mMIMO-U), a new technology that my colleagues and I have invented at Nokia Bell Labs, which maximises the spectrum reuse in the unlicensed bands, while enhancing the coexistence with neighbouring technologies.

mMIMO-U exploits the spatial awareness provided by the large number of antennas that we expect to install at the access points in the near future to create narrow beams, thin air wires, towards the intended users, while actively suppressing interference to and from coexisting neighbours.

This is done by using radiation nulls during the transmission phase, and a spatial interference rejection filter during the mandatory listen-before-talk phase. These radiation nulls and receive filter make the mMIMO-U node and neighbouring ones unaware of each other. They do not listen to or suffer from each other. This enables a more frequent medium access to both the mMIMO-U node and the neighbouring ones, which, in turn, results in an improved network performance and end-user quality of service.

What first stirred your interest in this area?

The annoying, poor performance of traditional Wi-Fi technology based on listen-before-talk in large venues such as conference halls, airports, bus stations, etc.

Who doesn’t experience this shortcoming of Wi-Fi when in a concert hall or a wedding venue? mMIMO-U, the technology that I am working on, is targeted at solving this problem by providing a cellular-like experience while running on unlicensed spectrum.

If there is such a thing, can you describe a typical day for you?

A day of work at Nokia Bell Labs can be very diverse, but I think it is always good to start with a routine.

In the mornings, I like to go to the gym, three or four times a week. Later, upon arrival at the office, I like to read the news, mostly Spanish. This helps me to keep connected with my country. Thereafter, I spend time answering all pending emails. I don’t like making my colleagues and collaborators wait for my answers.

Once the emails are done, I like to concentrate on the topic I am working on, which can vary: mathematical modelling, algorithm development, simulation of a given idea, etc. I try to find a block of at least four hours to work on those. During the day, it is also common to have on-site meetings with the managers and colleagues to discuss new ideas or the progress of the project we are working on.

Video conferences with some of my colleagues in other locations such as Stuttgart, Finland and the US are also part of my routine. This happens on demand as it’s important that the team is connected and that any issues are discussed as soon as possible, so that everyone is on the same page.

Towards the end of the day, I like to find 45 minutes to read some research papers or reports, just to keep connected with new ideas and trends. From time to time, I also like to go around the office and talk to the PhD students and newcomers. I like the new way of thinking from fresh graduates, as they see things differently. In the evening and at night, I like to disconnect, keep up with my hobbies, and spend time with family and friends.

What skills and tools do you use on a daily basis?

That really depends on the task that I am facing. There are days, when we are working in the creation of a concept, where I mostly use my telecommunication skills together with my theoretical and analytical skills to proof such concepts and assess whether the new idea can bring some benefits.

Other days, when we are working on the development of a concept, I mostly use my programming or implementation skills to study the proposed feature in detail in a variety of scenarios and under realistic assumptions. It is also important to use the ‘human’ skills daily to communicate and collaborate with my colleagues in an efficient manner.

What applications do you foresee for this research?

High-quality service provisioning in indoor scenarios and private venues where Wi-Fi technology is widely deployed, but tends to underperform.

It is easy to see that while cellular technology – such as 3G and 4G, based on licensed spectrum – is the most popular technology in outdoor scenarios, it is not in indoor ones, where Wi-Fi – based on unlicensed spectrum – is the most adopted one due to its reduced cost.

Moreover, in the case of private venues, both indoor and outdoor, owners are concerned about sharing sensitive data with cellular operators, and thus they prefer to manage and control their own networks using unlicensed spectrum and Wi-Fi technology.

Examples of indoor-private and outdoor-private scenarios are corporate buildings and large factories with multiple buildings. mMIMO-U can help to address this issue as it provides an enhanced quality of service, while still operating in the unlicensed spectrum.

Are there any common misconceptions about this area of research? How would you address them?

One misconception is that unlicensed spectrum is just unreliable by nature. However, it is not. It is the poor coordination mechanisms existing in current unlicensed technologies, the ones that prevent high spectral efficiencies in these bands.

When you first started work as a researcher, what were you most surprised to learn was important in the role?

The one thing that I did not expect that was so important is the ability to connect with others and the empathy that you must have towards the problems you are solving.

When you start your career as a researcher, you want to be that great guy that comes up with new and fantastic ideas, and can develop novel frameworks to prove and demonstrate them.

However, there is no such a thing, and the success of an invention depends on the collaborative effort of multiple people. Researchers with different backgrounds can interpret problems in a different manner and combine their different skills to create simple and elegant solutions.

Understanding and believing in the necessity of solving the problem you are tackling is also key.

What do you enjoy most about your career in research?

The thing that I enjoy the most about being a researcher is the endless and tough discussions with my colleagues and collaborators. I really enjoy those moments when we are discussing a topic, and we challenge each other with questions and examples.

It is always an enriching experience, as you think about things that you never thought before. I like when I walk out of a discussion and can explain some phenomena that I did not know about before. It is also very rewarding to see some of your ideas implemented into products that are running out there.

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